| Osain | |
| Other Name: | Osāin |
| Settlement Type: | Village |
| Pushpin Map: | India Bihar#India |
| Pushpin Map Caption: | Location in Bihar, India |
| Coordinates: | 25.5575°N 84.4095°W[1] |
| Subdivision Type: | Country |
| Subdivision Name: | India |
| Subdivision Type1: | State |
| Subdivision Name1: | Bihar |
| Subdivision Type2: | District |
| Subdivision Name2: | Bhojpur |
| Unit Pref: | Metric |
| Area Total Km2: | 0.480 |
| Elevation M: | 69 |
| Population Total: | 6308 |
| Population As Of: | 2011 |
| Population Density Km2: | auto |
| Demographics Type1: | Languages |
| Demographics1 Title1: | Official |
| Demographics1 Info1: | Bhojpuri, Hindi |
| Timezone1: | IST |
| Utc Offset1: | +5:30 |
| Postal Code Type: | PIN |
Osain is a village in the west-central part of Bihiya block in Bhojpur district, Bihar, India. As of 2011, its population was 6,308, in 966 households.[2]