A total 712 samples were collected from diarrhea patients in Saintpaul and Thanh nhan hospitals in Hanoi in period of January to August 2010. Eighthy four of Vibrio parahaemolyticus strains were isolated by culture method, corresponding to 11.80 per cent. These 84 strains belong to 11 serotypes of V. parahaemolyticus and 1 strain has untypeable K serotype. Also various serovars of the bacteria can cause infections, 03:K6 has been recognized as the predominance with 61 strains accounting for 72.6 per cent. Serotype 04:K8 and other 9 serotypes have only 11.9 and 1.2 to 2.4 per cent each serotype, respectively. All isolated strains were positive for the species-specific toxR gene. Although seventy-seven strains showed the typical biochemical characteristics of V. parahaemolyticus, but seven of these strains were changed the phenotype: one strain showed lysine decarboxylase test negative and six strains showed indole test negative. Most of V. parahaemolyticus isolates possess tdh gene (96.34 percent) while there was only 1 strain give possitve result for trh and other two strains negative for both of these gene. This results also suggest that molecular biology technique play an important role to detect virulence gen tdh and trh of V. parahaemolyticus for the confirmation of virulence strains, which cause diarrhea in human even of atypical strains in biochemical characteristics.