| Ajay River | |
| Name Etymology: | Sanskrit: Unconquerable |
| Pushpin Map: | India |
| Pushpin Map Caption: | Location of mouth |
| Subdivision Type1: | Country |
| Subdivision Name1: | India |
| Subdivision Type2: | State |
| Subdivision Name2: | Bihar, Jharkhand, West Bengal |
| Subdivision Type5: | Cities |
| Subdivision Name5: | Deoghar, Jamtara, Chittaranjan, Pandabeswar, Illambazar, Bhedia, Bolpur, Katwa |
| Length: | 300km (200miles) |
| Discharge1 Location: | Bhagirathi River |
| Source1 Location: | Jamui, Bihar |
| Source1 Coordinates: | 24.8494°N 86.5372°W |
| Source1 Elevation: | 400m (1,300feet) |
| Mouth Location: | Katwa, West Bengal |
| Mouth Coordinates: | 24.1019°N 88.2214°W |
| Mouth Elevation: | 21m (69feet) |
| Tributaries Right: | Pathro and Jayanti in Jharkhand, Tumuni and Kunur in Bardhaman district of West Bengal |
The Ajay (/ˈədʒɑɪ/) is a river which flows through the Indian states of Bihar, Jharkhand and West Bengal. The catchment area of Ajay River is 6000km2.[1]