Streptococcosis in cultured tilapia ( has increased during the past decade in China. In this study, a total of 248 strains were isolated from diseased tilapia, collected in the major tilapia-culturing area of China, during 2007-2015. The aim of the study was to analyze the characteristics of the 248 tilapia strains. In molecular characterization assays, four genotypic categories comprised of molecular serotype, multilocus sequence typing (MLST), virulence genes profiling patterns and prophage genotype, were used to analyze the genotypic diversity of these S. agalactiae strains were of molecular serotype Ia, and the remaining 19 were of type Ib. MLST revealed that all the serotype Ia strains were ST7, and all the serotype Ib strains were ST261. The results of virulence genes detection indicated that the 229 Ia-ST7 strains have the same genotype of virulence genes (V1), which carried 9 virulence genes (9/11: 81.8%), except that virulence genes were negative for them. The 19 Ib-ST261 strains have the same genotype of virulence genes (V2), which possessed 6 virulence genes (6/11: 54.5%) detected by PCR. Prophage detection suggested that the 229 Ia-ST7 strains could be divided into two genotypes: type P1 (36 strains) and P2 (193 strains). All the Ib-ST261 strains were negative for 10 prophage genes, and they belonged to type P3. According to the four molecular typing methods, all 248 strains could be divided into three genotypes: namely, Ia-ST7-V1-P1, Ia-ST7-V1-P2, and Ib-ST261-V2-P3. Notably, the predominant strains of in China had shifted from type Ia-ST7-V1-P1 to type Ia-ST7-V1-P2 during 2010-2011. In addition, the type Ia-ST7-V1-P1 strain was predominant before 2011, and the type Ia-ST7-V1-P2 strain predominated thereafter. In conclusion, the strains collected from tilapia in China showed low genetic diversity. Through analyses of the characteristics of the strains isolated from deceased tilapia in the major tilapia-culturing area of China, we can deduce that the transmission of relies on the import of either new tilapia stock or culture water.