| JAERI | Japan Atomic Energy Research Institute |
| JAK | JAnus Kinase |
| JAMA | Journal of the American Medical Association |
| JASSM | Joint Air to Surface Standoff Missile |
| JDA | Joint Development Agreement |
| JIA | Juvenile Idiopathic Arthritis |
| JIS | Japan International Standard |
| JP | JaPan |
| JRF | Jet Reference Fluid |
| JV | Joint Venture |