| Obaix |
| Obigies |
| Obourg |
| Ochamps |
| Ocquier |
| Odeigne |
| Odeur |
| Œudeghien |
| Offagne |
| Ogy |
| Ohain |
| Ohey |
| Oizy |
| Ollignies |
| Olloy-sur-Viroin |
| Olne |
| Omal |
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| On |
| Onhaye |
| Onoz |
| Ophain-Bois-Seigneur-Isaac |
| Opheylissem |
| Opont |
| Opprebais |
| Orbais |
| Orchimont |
| Oreye |
| Ormeignies |
| Orp-le-Grand |
| Orroir |
| Ostiches |
| Othée |
| Otrange |
| Ottignies |
| Ougrée |