| En Name: | Tosu |
| Ru Name: | Тосу |
| Other Name: | Халбаакы |
| Other Lang: | Sakha |
| Coordinates: | 63.8778°N 121.6342°W |
| Map Label Position: | left |
| Federal Subject: | Sakha Republic |
| Adm District Jur: | Vilyuysky District |
| Adm Selsoviet Jur: | Khalbakinsky Rural Okrug |
| Adm Selsoviet Type: | Rural okrug |
| Adm Ctr Of: | Khalbakinsky Rural Okrug |
| Inhabloc Cat: | Rural locality |
| Inhabloc Type: | Selo |
| Mun District Jur: | Vilyuysky Municipal District |
| Mun District Jur Ref: | [1] |
| Rural Settlement Jur: | Khalbakinsky Rural Settlement |
| Mun Admctr Of: | Khalbakinsky Rural Settlement |
| Pop 2010Census: | 665 |
Tosu (ru|Тосу; sah|Халбаакы, Xalbaakı) is a rural locality (a selo), the administrative centre of and one of two settlements, in addition to Starovatovo, in Khalbakinsky Rural Okrug of Vilyuysky District in the Sakha Republic, Russia. It is located 18km (11miles) from Vilyuysk, the administrative center of the district. Its population as of the 2010 Census was 665,[2] of whom 325 were male and 340 female, down from 731 as recorded during the 2002 Census.[3]