| Ose Immunotherapeutics | |
| Osimatic S.A.S. | Yvelines |
| OSInet | Essonne |
| Osium AI | |
| Osivax | |
| OSO-AI | |
| OSS Ventures | |
| Osta Therapeutics | |
| Ostendi | Hauts-de-Seine |
| OT4B S.A.S. | |
| Otaree | |
| Otidea | Hautes-Pyrénées |
| Otium Capital | |
| Otovo France S.A.S. | |
| OTSTC - Creative BIometric | Paris |
| Ouebsson | Loire-Atlantique |
| Ouest Communications Mobiles | Vienne |
| Ouest France - Start-up | Ille-et-Vilaine |
| Ouest-PC | Ille-et-Vilaine |
| OuestWare | |
| Ouidev | |
| Ouidou | |
| Ouishare | Seine-Saint-Denis |
| Ouroboros Telecom | |
| Ourouk | Paris |
| Outiref | Bas-Rhin |
| Outmind | |
| Outsight S.A. | Paris |
| Outsourcia | Hauts-de-Seine |
| Outsourcing Network Intelligence S.A.S. | Val-d'Oise |
| OutWit Technologies | Hauts-de-Seine |
| Ouvaton | |
| Ouvrez la boite | Bouches-du-Rhône |
| OVEA | Hérault |
| Oveanet | Hérault |
| Oveliane | Hauts-de-Seine |
| Over-Link S.A.S. | Alpes-Maritimes |
| OverBlog | Haute-Garonne |
| Overscan | Puy-de-Dôme |
| OVH Télécom | Nord |
| OVHcloud | |
| Ovio Optics | Eure |
| Ovotor | |
| OW2 Consortium | Paris |
| Owea S.A.R.L. | Calvados |
| Owlblack | |
| Owlint | |
| OWN | |
| Ownpage | |
| Oxade Consulting | Paris |