Abstract: Objective To study the carriage, growth and decline of Vibrio parahaemolyticus in diarrhea patients, establish molecular tracing methods, detect predominant types in epidemics and analyze related factors of the infection for the prevention and control of food poisoning caused by V. parahaemolyticus. Methods V. parahaemolyticus were isolated by screening method from diarrhea patients. The isolated strains were identified by using API biochemistry identification system and grouped with serum agglutination test. The drug susceptibility was detected with K-B method. Molecular characteristics were detected by using pulsed field gel electrophoresis (PFGE). Toxic genes were detected by using polymerase chain reaction (PCR). Results Totally 901 strains of V. parahaemolyticus were isolated from 6216 samples, accounting for 63.45% of the pathogens detected. The biological characteristics of the V. parahaemolyticus strains detected was typical. The resistance rates of the strains to ampicillin and penicillin were high, but low to other antibiotics. Six serogroups were found in 480 strains of V. parahaemolyticus, serogroup O∶3 accounted for 72.71%, which was predominant. PFGE pattern analysis indicated that the strains could be classified into 19 types, but the strains from food samples shared similar PFGE patterns There were 396 strains carrying tdh gene (70.71%), 79 strains carrying trh gene (14.11%) and 18 strains carrying both tdh gene and trh gene (3.21%). Totally 365 strains carrying tdh gene were positive in Kanagawa test (73.14%). Conclusion Diarrhea is mainly caused by V. parahaemolyticus infection in Ningbo. O∶3 is the predominant serotype. PFGE is an accurate, reliable and specific method, which is suitable to identify infection source and find transmission route. Most strains isolated from patients carry toxic genes, which are different with the strains from see food and environment and -lactm antibiotics; aminoglycosides and quinolone can be used in clinical treatment.