| C.Y.S. ENGINEERING COMPANY LIMITED | Private company limited by shares | Live |
| CYSC COMPANY LIMITED | Private company limited by shares | Live |
| Cysco HK Limited | Private company limited by shares | Live |
| CYSD TECHNOLOGY LIMITED | | Live |
| HONG KONG CYSEA INTERNATIONAL TRADE CO., LIMITED | Private company limited by shares | Live |
| Cysec Limited | Private company limited by shares | Live |
| SAFECAP (CYSEC) LIMITED | Private company limited by shares | Live |
| CYSECURITY ELECTRONIC LIMITED | Private company limited by shares | Live |
| CYSL ENGINEERING LIMITED | | Live |
| Cyson Advisors Limited | | Live |
| CYSPO TECHNOLOGY (HONGKONG) CO., LIMITED | Private company limited by shares | Live |
| CYSTAGELIGHT HK LIMITED | Private company limited by shares | Live |
| CYSTAL ON ENTERPRISE LIMITED | Private company limited by shares | Live |
| CYSTAL PLACE INVESTMENT LIMITED | Private company limited by shares | Dissolved |
| CYSTECH ELECTRONICS (HK) LIMITED | Private company limited by shares | Dissolved |
| CYSTM LIMITED | Private company limited by shares | Live |
| cystron technology Limited | Private company limited by shares | Live |
| CYSW CONSULTING LIMITED | Private company limited by shares | Live |
| C.Y.S.W.L. LIMITED | Private company limited by shares | Live |