| Joho Technology, Inc. | Tokyo |
| Johodai | |
| Johokobo, Inc. | |
| JOMON Internet Service | Tokyo |
| Jorte, Inc. | |
| Josai International University | |
| Josai University | |
| Josai University - Department of Mathematics | Saitama |
| JP Domains | Tokyo |
| JPDirect | Tokyo |
| JPRS Registrar Co., Ltd | Tokyo |
| JPServe | Tokyo |
| JPstream | Tokyo |
| JR East Net Station Co., Ltd | Tokyo |
| JRC Nihon Musen | Tokyo |
| JS Systems Co., Ltd | Tokyo |
| JSE Corporation | Aomori |
| JSR Corporation | Tokyo |
| Jstyle | Tokyo |
| JTEKT Corporation | |
| Jumonji University | |
| Junshin Gakuen University | |
| Junshin Junior College | |
| Juntendo University | Tokyo |
| Jupiter Telecommunications Co., Ltd | Tokyo |
| Jurio Co., Ltd | Tokyo |
| Justice Technologies | Tokyo |
| JustInCase | |
| justInCase Technologies Co., Ltd | Tokyo |
| JV-IT Holdings Co., Ltd | Tokyo |
| JVCKENWOOD Corporation | Tokyo |
| JWord | Tokyo |
| J’s Communication Co., Ltd | Osaka |
| J’s Technology Co., Ltd | Tokyo |
| K.mecs Co., Ltd | |
| Kabuku, Inc. | |
| Kacho College | |
| Kaetsu University | |
| Kaga Electronics Co., Ltd | Tokyo |
| Kagawa Prefectural University of Health Sciences | |
| Kagawa University | |
| Kagoshima Prefectural College | |
| Kagoshima University | |
| Kagoshima Women's College | |
| Kaichi International University | |
| KAIJO Corporation | Tokyo |
| Kakao Piccoma Corporation | |
| Kaken Pharmaceutical Co., Ltd | |
| Kamakura Women’s University | |
| Kameda University of Health Sciences | |