--- title: "MUJI Smooth Oil Ink Ballpoint Pen: 0.38, 0.5, 0.7 mm" canonical: "https://stationerytimes.com/guides/muji-smooth-oil-ink-ballpoint-pen/" description: "MUJI Smooth Oil Ink Ballpoint Pen explained: 0.38, 0.5 and 0.7 mm balls, 14.1 cm long, grip to the tip, interchangeable refills, price band and origin." category: "Pens" type: "Ballpoint pen" published: 2026-11-01 updated: 2026-11-01 author: "Ellis Penhale" publisher: "Stationery Times" sources: 3 products: - name: "MUJI Smooth Oil Ink Ballpoint Pen 0.5 mm" brand: "MUJI" brand_origin: "Japan" made_in: "Japan" material: "Tip: polypropylene and thermoplastic elastomer; shaft: ABS resin (per MUJI USA)" price_band: "$ (under $5 per pen (multi-packs divided by the count), typical US retail, October 2026)" manufacturer: "Ryohin Keikaku Co., Ltd." model: "Smooth Oil Ink Ballpoint Pen 0.5 mm - Black (NBE04A3A)" gtin: "4550583768157" url: "https://www.muji.us/products/smooth-oil-ink-ballpoint-pen-0-5-mm-black-nbe04a3a" --- # MUJI Smooth Oil Ink Ballpoint Pen: 0.38, 0.5, 0.7 mm > The MUJI Smooth Oil Ink Ballpoint Pen is a quick-drying oil-ink ballpoint with a grip that runs to the tip. MUJI USA lists the 0.5 mm at 14.1 cm (5.6 in), sells it in 0.38, 0.5 and 0.7 mm, says refills are interchangeable between single-color and multi-color bodies, and gives Japan as the origin. - URL: https://stationerytimes.com/guides/muji-smooth-oil-ink-ballpoint-pen/ - Category: Pens - Author: Ellis Penhale - Published: 2026-11-01 - Updated: 2026-11-01 ![MUJI Smooth Oil Ink Ballpoint Pen 0.5 mm drawn to scale at 14.1 cm with a dark grip running to the tip](https://stationerytimes.com/images/raster/muji-smooth-oil-ink-ballpoint-pen-illustration-16x9.png?v=c2ee53fe) *The 0.5 mm pen at MUJI USA's listed 14.1 cm (1 mm = 6.2 px).* Original illustration made for this guide. © Stationery Times. Original drawing (SVG): . Drawings © 2026 Stationery Times, reusable with credit under CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). ## Product facts | Product | Brand | Brand origin | Made in | Material | Released | Price range (typical US retail, October 2026) | |---|---|---|---|---|---|---| | MUJI Smooth Oil Ink Ballpoint Pen 0.5 mm | MUJI (by Ryohin Keikaku Co., Ltd.) | Japan | Japan | Tip: polypropylene and thermoplastic elastomer; shaft: ABS resin (per MUJI USA) | – | $: under $5 per pen (multi-packs divided by the count) | - Made in (MUJI Smooth Oil Ink Ballpoint Pen 0.5 mm): Japan. MUJI USA's product details give "Country/Region of Origin: Japan" for the 0.5 mm black pen. Source: https://www.muji.us/products/smooth-oil-ink-ballpoint-pen-0-5-mm-black-nbe04a3a - Good for: Everyday writing, Note-taking. ## Key takeaways - MUJI USA lists the 0.5 mm pen at 5.6 in (14.1 cm) long; the 0.38, 0.5 and 0.7 mm sizes come in black, red and blue. - MUJI says the oil ink is quick-drying and the grip extends all the way to the tip. - The tip is polypropylene with thermoplastic elastomer and the shaft is ABS resin. - MUJI says the refills are interchangeable, so single-color, four-color and three-color-plus-pencil bodies share them. - MUJI USA gives Japan as the origin, and each single pen is in our $ band (under $5). ## What is the MUJI Smooth Oil Ink Ballpoint Pen? **It's a quick-drying oil-ink ballpoint with a rubber-like grip that runs all the way to the tip, in three ball sizes.** MUJI is the brand of Ryohin Keikaku, the Japanese retailer. MUJI USA says the pen gives an ultra-smooth writing experience; that is the maker's claim. The same family includes four-color bodies and three-color bodies with a mechanical pencil, all in the same sizes. ## MUJI smooth oil ink pen specs | Spec | Value | |---|---| | Maker | MUJI (Ryohin Keikaku Co., Ltd.), Japan | | Type | Ballpoint pen, refillable | | Length (0.5 mm black) | 5.6 in (14.1 cm) | | Ball sizes | 0.38, 0.5, 0.7 mm | | Ink | Oil-based, quick drying | | Materials | Tip: polypropylene, thermoplastic elastomer; shaft: ABS resin | | Colors (single pens) | Black, red, blue | | Barcode (0.5 mm black) | 4550583768157 | | Made in | Japan (MUJI USA) | MUJI USA gives no weight or barrel width, so the barrel in our drawing is drawn by eye. ## Who is the MUJI smooth oil ink pen for? **It suits people who want a smooth ballpoint with a grip and the freedom to mix refills.** - **Everyday writing:** MUJI USA says the quick-drying oil ink and interchangeable refills suit everyday use, in our $ band. - **Note-taking:** it writes a 0.5 mm line with quick-drying oil ink, and a 0.38 mm size is also sold. Skip it if you write while lying down: MUJI warns against using the pen with its tip pointing upwards. ![Bars at 20 times scale showing the 0.38, 0.5 and 0.7 mm ball sizes](https://stationerytimes.com/images/muji-smooth-oil-ink-ballpoint-pen-ball-sizes.svg?v=d9d387a9) *The three ball sizes MUJI USA lists (nominal widths at 20×). Original illustration made for this guide. © Stationery Times.* ## Which ball size should you choose? **Choose 0.38 mm for small notes in planners, 0.5 mm for everyday writing, and 0.7 mm for a bolder line.** The three sizes are the ones MUJI USA lists; the figure above shows their nominal widths. The same three sizes exist in MUJI's [cap-type gel pen](https://stationerytimes.com/guides/muji-gel-ink-pen/), which uses gel ink. ## How do the interchangeable refills work? **MUJI says the refills can be freely combined across its single-color, four-color and three-color-plus-pencil bodies.** In the US it sells the three-color-plus-pencil pens in 0.38, 0.5 and 0.7 mm, and four-color pens in the same sizes. MUJI USA also sells refills singly in green, blue and other colors. ## How does it compare with MUJI's other ballpoints? **It's the grippy, multi-size choice; the [oil ink polycarbonate pen](https://stationerytimes.com/guides/muji-oil-ink-polycarbonate-ballpoint-pen/) is a thick, plain 0.7 mm pen.** | | Smooth Oil Ink | Oil Ink Polycarbonate | |---|---|---| | Length | 14.1 cm (5.6 in), 0.5 mm | 14.0 cm (5.5 in) | | Ball sizes | 0.38 / 0.5 / 0.7 mm | 0.7 mm | | Grip | To the tip | Plain barrel | | Made in | Japan | Japan | See our [best ballpoint pens](https://stationerytimes.com/guides/best-ballpoint-pens/) for ballpoints from other brands. ## Where is it made, and what does it cost? **In Japan: MUJI USA gives Japan as the country or region of origin.** Each single pen is in our $ band, under $5. MUJI USA sells it as Final Sale, with no refunds or exchanges; we read the page on November 1, 2026, and prices change. ## Frequently asked questions ### What sizes does the MUJI smooth oil ink pen come in? MUJI USA lists 0.38, 0.5 and 0.7 mm in black, red and blue, plus four-color and three-color-with-pencil versions. ### Can you combine MUJI smooth oil ink refills in one body? MUJI USA says the refills are interchangeable, so single-color, four-color and three-color-plus-mechanical-pencil options can be freely combined. ### Does the MUJI smooth oil ink pen have a grip? Yes. MUJI USA says the grip at the bottom of the pen extends all the way to the tip so the pen doesn't slip. ### Can you write upside down with the MUJI oil ink pen? MUJI USA's care notes say not to use the pen with its tip pointing upwards, for example when writing on a wall calendar or lying down. ### Is the MUJI smooth oil ink pen made in Japan? Yes. MUJI USA lists Japan as the country or region of origin. ### Is the MUJI 0.38 mm oil ink pen finer than the gel pen? The ball is the same nominal size as MUJI's 0.38 mm cap-type gel pen. Oil ink and gel ink lay down lines differently, so we can't say which looks finer until we test them. ### Can I return a MUJI pen bought online? MUJI USA marks it Final Sale, with no refunds or exchanges, on its product page as we read it. ## Sources - [MUJI USA: Smooth Oil Ink Ballpoint Pen 0.5 mm - Black (length 5.6 in / 14.1 cm; nib 0.5 mm; oil-based ink; materials; care notes; Japan; read in full November 1, 2026)](https://www.muji.us/products/smooth-oil-ink-ballpoint-pen-0-5-mm-black-nbe04a3a) - [MUJI USA: Smooth Oil Ink 4-Color Ballpoint Pen 0.5 mm (listing seen in the stationery collection)](https://www.muji.us/products/smooth-oil-ink-4-color-ballpoint-pen-0-5-mm-nbe12a3a) - [MUJI USA stationery collection (product list, read November 1, 2026)](https://www.muji.us/collections/stationery)