This study aimed to investigate the effects of feeding diets supplemented with Lactobacillus plantarum LP-37 and Pediococcus pentosaceus PP-23 on the growth and immune performance of Nile tilapia. Seven experimental groups were used in this study, namely, control group C0: feeding basic feed; L1-L3 groups: adding three different concentrations of Lactobacillus plantarum LP-37 (1.0×10⁶ CFU/g, 1.0×10⁷ CFU/g, 1.0×10⁸ CFU/g) to basic feed; P1-P3 groups: adding three different concentrations of Pediococcus pentosaceus PP-23 (1.0×10⁶ CFU/g, 1.0×10⁷ CFU/g, 1.0×10⁸ CFU/g) to basic feed. The results showed that except for those in the L1 group, the final body weights of the fish in the experimental groups (123.22~158.60 g) were significantly higher than those of the C0 group fish (118.16±4.88) g (P＜0.05). Except for those in the L1 and P1 groups, the weight gain rates in the other experimental groups (128.69~156.20 g) were significantly higher than that in the C0 group (10⁸.16±0.45)% (P＜0.05). The final body weight and weight gain rate of the fish in the L3 [(150.00±6.66) g, (152.69±3.51)%] and P2 [(153.24±5.36) g, (143.12±5.23)%] groups were significantly higher than those of the C0 group fish (P＜0.01). The addition of different concentrations of LP-37 and PP-23 was able to improve activities of three digestive enzymes of Nile tilapia. Among various groups, the greatest increases appeared in the L3 and P2 groups. In L3, protease (PRS) was (1.39±0.06) U/mg, α-amylase (AMS) was (55.20±3.39) U/dL, and alkline phosphatase (AKP) was (3.28±0.28) U/L. In P2, PRS was (1.40±0.04) U/mg, α-amylase (AMS) was (65.28±11.50) U/dL, and alkaline phosphatase (AKP) was (3.50±0.36) U/L. Compared with the expression in the C0 group, IL-1β and IFN-γ genes in the spleen of the fish in the experimental groups were significantly down-regulated (P＜0.05), and the highest down-regulation occurred in the L3 and P2 groups. IL-1β gene in the head kidney of fish of various experimental groups was also significantly down-regulated (P＜0.05), and the highest down-regulation occurred in the L3 and P2 groups. In terms of intestinal tissue morphology, the villous height in various experimental groups was significantly higher than that in the C0 group (P＜0.05). The crypt depth, the ratio of villous height to crypt depth, and muscle layer thickness in the L3 and P2 groups were significantly higher than those in the other experimental and control groups (P＜0.05), whereas there was no significant difference in these parameters between the other experimental and control groups (P＞0.05). In summary, adding 1.0×10⁸ CFU/g Lactobacillus plantarum LP-37 and (1.0×10⁷ ) CFU/g Pediococcus pentosaceus PP-23 to the diet can significantly increase the growth rate, digestive enzyme activity, and intestinal tissue structure, and alter the expression of certain immune related genes in Nile tilapia.