| CELSYS, Inc. | Tokyo |
| CEN Solutions Corporation | Tokyo |
| Center for Educational Computing | Tokyo |
| Central Institute for Experimental Medicine and Life Science | |
| Central Research Institute of Electric Power Industry | |
| Central soft Co., Ltd | Tokyo |
| Century Techno Co., Ltd | Tokyo |
| Cerma Precision Co., Ltd | Tokyo |
| CES Co., Ltd | Fukuoka |
| Cessios Co., Ltd | Tokyo |
| CGI Rescue | Tokyo |
| Chacha Web Design Kyoto | Kyoto |
| Chaintope, Inc. | |
| Chama-Net | Kanagawa |
| Chiba Institute of Science | |
| Chiba Institute of Technology | |
| Chiba Keizai University | |
| Chiba University | |
| Chiba University - Department of Mathematics and Informatics | Chiba |
| Chiba University of Commerce | |
| Chibagin Computer Service | Chiba |
| Chichibu-Internet | Tokyo |
| Chikushi Jogakuen | |
| Chinasoft-Tokyo Corporation | Tokyo |
| Chiome Bioscience Co., Ltd | Tokyo |
| Chiptip Technology Co., Ltd | Tokyo |
| Chitose Institute of Science and Technology | |
| Chordia Therapeutics, Inc. | |
| Chowdhury Software Services, Inc. | Tokyo |
| Chubu Electric Power Co., Inc. | |
| Chubu Telecommunications Co., Ltd | Tokyo |
| Chubu University | |
| Chugai Pharmaceutical Co., Ltd | |
| Chukyo Gakuin University | |
| Chukyo University | |
| Chuo Electronics Co., Ltd | Tokyo |
| Chuo Gakuin University | |
| Chuo System Corporation | Tokyo |
| Chuo University | |
| Chuo University - Department of Mathematics | Tokyo |
| CIBIS, Inc. | Tokyo |
| Cincom Systems Japan Ltd | Tokyo |
| Cinnamon Co., Ltd | Tokyo |
| Cipher Cipher Co., Ltd | Tokyo |
| CKD Corporation | |
| CKD NIkki Denso Co., Ltd | |
| Claps Co., Ltd | Tokyo |
| Claytechworks Co., Ltd | Tokyo |
| ClickAccess | Tokyo |
| ClickNet Co., Ltd | Tokyo |