Abstract: A 2-year on-farm experiment was conducted under rainfed condition to study the effect of Rhizobium inoculation (with or without chemical fertilizer) and chemical fertilizer ( 0 and 50-30-20 Kg ha -1 P2O5, K2O and S) on cowpea. Two sources of biofertilizer were used. Biofertilizer showed significantly higher yield attributes and seed yield of cowpea as compared to control. Biofertilizer of BARI source gave the highest cowpea seed yield (880 Kg ha -1) and the lowest seed yield (658 Kg ha -1) was obtained without biofertilizer. No significant difference was found between the two sources of bio-fertilizer. Chemical fertilizer showed better performance than control in case of seed yield and all yield contributing characters of cowpea. Interaction of bio-fertilizer and chemical fertilizer also showed statistically significant difference. PKS with biofertilizer of both BAU and BARI sources gave the highest seed yield (987 Kg ha -1) and the lowest seed yield (525 Kg ha -1) was obtained from control treatment. Though the highest average rate of return (4556%) was found using biofertilizer of BARI source but on consideration of net return and also soil health, PKS with biofertilizer of BARI source where ARR was the second highest may be suggested for growing cowpea under rainfed condition.