Abstract: Cultural and nutritional conditions were optimized for indole acetic acid (IAA) production by a newly isolated Rhizobium sp. from the root nodules of Vigna mungo (L.) Hepper. The isolate produced high amount of IAA (40 mg L-1) when medium was supplemented with L-tryptophan over D-or DL-tryptophan isomer at pH 7.2. The effects of different carbon sources and nitrogen sources on indole acetic acid production were studied. IAA production increased upto 1.4 fold over control when the medium was supplemented with glucose (1%) and KNO3 (0.2%). The tryptophan (1568±22.47 μg g-1 fresh tissue) and IAA (6.34±0.18 μg g-1 fresh tissue) levels were found to be higher in young and healthy root nodules than normal non-nodulated roots. The results indicated that the symbiont might provide high level of IAA to root nodules.