| Asahigakuen | |
| Asahikawa City University | |
| Asahikawa Medical University | |
| AsahiNet | Tokyo |
| Asakurasoft Co., Ltd | Tokyo |
| Asama Software Corporation | Nagano |
| Asapnetwork Co., Ltd | Tokyo |
| Ascent Development Services | Tokyo |
| Ascent Robotics Co., Ltd | Tokyo |
| Ascentech Co., Ltd | Tokyo |
| Asco Japan Co., Ltd | Hyogo |
| Ash Multimedia Lab | Tokyo |
| Ashikaga University | |
| Ashiya University | |
| Asia Commerce Ltd | Tokyo |
| Asia Pacific Computer Emergency Response Team | Tokyo |
| Asia Pacific Networking Group | Hiroshima |
| Asia University | |
| Asial Corporation | Tokyo |
| Asian Growth Research Institute | |
| Asian Productivity Organization | |
| AsiaQuest Co., Ltd | Tokyo |
| ASIOT Co., Ltd | Tokyo |
| ASJ | Tokyo |
| Ask Co., Ltd | Tokyo |
| ASKA Pharmaceutical Co., Ltd | |
| Asobie Co., Ltd | Tokyo |
| ASOBIMO Co., Ltd | Tokyo |
| ASP i-do | Tokyo |
| Asteria Corporation | |
| ASTI Corporation | Shizuoka |
| ASTOM R&D | Saitama |
| Astro Terrace, Inc. | |
| Astrodesign, Inc. | Tokyo |
| Astroscale Holdings, Inc. | |
| Asuka Index Co., Ltd | Tokyo |
| Asukanet Co., Ltd | |
| Asuzac Co., Ltd | Nagano |
| Asware Co., Ltd | Tokyo |
| AT Partners Co., Ltd | Tokyo |
| AT System | Tokyo |
| At-Link | Tokyo |
| AtCoder Co., Ltd | Tokyo |
| Atelier Ishikawa Co., Ltd | Kanagawa |
| ATL Systems, Inc. | Tokyo |
| Atlan Corporation | Tokyo |
| Atlus Co., Ltd | Tokyo |
| Atmark Corporation | Tokyo |
| atmarkIT | Tokyo |
| Atom Co., Ltd | Tokyo |