Background: The application of probiotics to aquaculture is rather new. Probiotics affect the intestinal microbial flora of fish and subsequently modulate its immune response and growth performance. OBJECTIVES: This study was conducted to evaluate the effect of food supplementation with L.plantarum and L.bulgaricus on growth performance and gut microbiota of Cyprinus carpio. METHODS: For this purpose, 480 juveniles of C. carpio (40.2 ±6.3 gr Mean ±SD) were randomly divided into three equal groups (each group in three replicates) and fed with diet containing 5×107 cfu g_1 of Lactobacillus plantarum (group A), Lactobacillus bulgaricus (group B) and control diet (group C) for 60 days. To evaluate the persistent presence of the bacteria and their effects on the microbiota of the digestive system, remained fish of each group were fed with free probiotic diet from day 60 to 75. RESULTS: Results showed that most growth indices of probiotic treated groups were increased compared to control group in all sampling points. Although FCR decreased significantly in Groups A (2.9±0.43) and B (2.75±0.37) compared to control (3.88±0.52), SGR, WGP and DWG increased only in Group B compared to control group (P0.05). Intestinal lactobacillus ratio at days 30 and 60 was significantly higher than the control group (P<0.05). Group B showed the highest lactobacillus rate among the groups at day 30. Total intestinal bacteria count on day 30 and 60 were significantly higher in probiotic-treated fish compared to the control group (P<0.05). CONCLUSIONS: It can be concluded that L.bulgaricus can promote growth indices and intestinal Lactic acid bacterial proportion in common carp. Then it can be a proper candidate for a probiotic in common carp after more trials in farm scale.