Objective To investigate the contamination of Vibrio parahaemolyticus in Portunus trituperculatus in Shanghai and Ningbo retail markets and to assess the public health risks induced by V. parahaemolyticus. Method The counts of V. parahaemolyticus in Portunus trituperculatus were determined by the most probable number (MPN) technique. The consumption pattern of Portunus trituperculatus was investigated in Shanghai residents by retrospective dietary survey. The semi-quantitative risk assessment for V. parahaemolyticus in Portunus trituperculatus was made by a software of Risk Ranger. Result V. parahaemolyticus was isolated from 60.5% (23/38) of samples from Shanghai while 13.3% (4/30) from Ningbo with a mean of 0.75MPN/g and 5.50MPN/g respectively in positive samples. The daily intake of Portunus trituperculatus for a Shanghai resident was 2.95 g/d. The relative risk for V. parahaemolyticus in Portunus trituperculatus was 36. The probability of illness caused by V. parahaemolyticus in Portunus trituperculatus per day per consumer of interest was 8.22×10-9, and the total predicted patients per annum in the population of interest was 42.5 cases. Changing the selection of some risk factors in the model, the risk from the consumption of Portunus trituperculatus decreased for 10 times if good control measures were taken. Conclusion V. parahaemolyticus is frequently found in Portunus trituperculatus in Shanghai retail markets, which may cause higher risks to public health. Therefore, strengthening surveillance in the future is necessary.