| Japan System Control Co., Ltd | Tokyo |
| Japan Technical Software Co., Ltd | Tokyo |
| Japan Telework Association | Tokyo |
| Japan University of Economics | |
| Japan University of Health Sciences | |
| Japan UNIX Society | Tokyo |
| Japan Venture Capital Association | |
| Japan Women's University | |
| Japan-Net | Tokyo |
| Japan-nic.ac | Tokyo |
| Japanese Foundation for Cancer Research | |
| Japanese Red Cross College of Nursing | |
| Japanese Red Cross Toyota College of Nursing | |
| Japanese Society for Artificial Intelligence | Tokyo |
| Japanese Society of Computational Statistics | Tokyo |
| Jastec Co., Ltd | Tokyo |
| Java basics | Tokyo |
| JavaDrive | Tokyo |
| JBC Holdings Co., Ltd | |
| JC Electronics Corporation | Tokyo |
| JCC Engineering Co., Ltd | |
| JCNT Co., Ltd | Tokyo |
| JCR Pharmaceuticals Co., Ltd | |
| JEL Corporation | Hiroshima |
| Jet Studio Co., Ltd | Tokyo |
| JETBOY | |
| Jetsoft | Tokyo |
| JFE Systems, Inc. | Tokyo |
| JH Lab Co., Ltd | Tokyo |
| Jibannet Co., Ltd | Tokyo |
| Jichi Medical University | |
| jig.jp | Tokyo |
| JIITAK | |
| Jij Co., Ltd | Tokyo |
| Jikei University | |
| Jiksak Bioengineering Co., Ltd | Kanagawa |
| Jin-ai University | |
| Jin-ai Women's College | |
| JIPDEC | Tokyo |
| Jiraffe | |
| JISA | Tokyo |
| Jissen Women's Educational Institute | Tokyo |
| Jitsubo Co., Ltd | Kanagawa |
| JMACS Japan Co.,Ltd. | |
| JNP-Aventures Co., Ltd | |
| Jobcan Kaikei Co., Ltd | Tokyo |
| Jobu University | |
| Jocavio Co., Ltd | |
| Joetsu University of Education | |
| Johnson & Co., Ltd | Tokyo |