The present study was carried out to evaluate growth promoting effect of commercial probiotic Biosyn on the fingerlings of Indian major carp, Labeo rohita. The fingerlings weighing 7.239�0.232 g were distributed randomly into four treatment groups T , T , T and T of 15 fishes each in triplicate. Four Isoproteinous experimental diets 0 1 2 3 were prepared by mixing rice bran, deoiled mustard oil cake, deoiled soybean cake and vitamin-mineral mixture. The probiotic Biosyn was incorporated into diet D @ 0.2%, D @ 0.4% and D @ 0.6%. In control diet D , Biosyn was not in- 1 2 3 0 corporated. T group fishes were fed with D diet, T with D , T with D , T with D @ 5% body weight per day for 90 0 0 1 1 2 2 3 3 days. The water quality parameters were regularly monitored. Fingerlings fed with diet D achieved higher specific 3 growth rate (SGR 0.648%), gross conversion efficiency (GCE 0.299), condition factor (CF 1.91) and better feed conversion ratio (FCR 3.255) as compared to other treatments. The obtained results indicated that T was the best treat- 3 ment which realized significant (P