Abstract: To evaluate molecular genetic relationships, genetic differentiation and gene flow among the introduced populations of Nile tilapia (Oreochromis niloticus) in mainland China, 12 pairs of polymorphic microsatellite primers were used to analyze genetic relationships among 10 populations of Oreochromis niloticus (one indigenous population in Egypt as the control group, nine introduced populations in mainland China as experimental group). The measures of genetic distanceD_A, D_C, D_SW, (δμ)² showed that the genetic distance between EGY and USA was smallestD_A=0.2174, D_C=0.4140, D_SW=0.8769, (δμ)²=22.6904. The measures of D_A and D_C showed that the maximum genetic distance was between GD and XJF (D_A=0.5851, D_C=0.6789). The measures of D_SW and (δμ)² showed that the maximum genetic distance was between USA and XJFD_SW=4.0907, (δμ)²=138.18. The measures of F_ST and R_ST showed that genetic differentiation between EGY and GD was the minimum (F_ST=0.0326, R_ST=0.0337), and genetic differentiation between XJF and LY were the maximum (F_ST=0.2098, R_ST=0.2655). There were significant genetic differences between all pairs of populations (P < 0.05). Clustering relationship between populations showed that WY, GD, EGY and USA population were clustered together; BL, LY and EW population were clustered together; JNM and GLD population were clustered together. XJF population was clustered into an independent branch. Bayesian clustering analysis showed that 10 populations were clustered into two categories with XJF, BL, LY and EW in the first category population and others in the second category. The results of phylogenetic tree and Bayesian clustering analysis were supported by analysis of molecular variance and principal components analysis. The average values of historical gene flow among populations were evaluated on the basis of F_ST and R_ST, which were 2.4427 and 2.1983, respectively. Results of recent gene flow among populations showed that the first generation migrants in each population was 0-7, accounting for 0 to 23.3% of total samples. Overall, significant genetic difference was detected among introduced populations of Nile tilapia in China. And there is some historical gene flow and recent gene flow among populations. This study provided a scientific basis for protection and utilization of germplasm resources of introduced populations of Nile tilapia in China.