Vibrio parahaemolyticus is a human pathogen that naturally inhabits marine and estuarine environments. Infection with V. parahaemolyticus is often associated with the consumption of raw or undercooked seafood, causing gastroenteritis with watery diarrhea. The presence of two type III secretion system (T3SS) proteins, thermostable direct hemolysin (TDH) and TDH-related hemolysin (TRH), has been closely associated with the severity of diarrheal illness. TDH and TRH have various biological activities including hemolytic activity, cardiotoxicity, and enterotoxicity. T3SS1 is involved in cytotoxicity to host cells and orchestrates a multifaceted host cell infection by induction of autophagy, cell rounding, and cell lysis. T3SS2 is thought to be related to the enterotoxicity of V. parahaemolyticus. The activities of inducing diarrhea of each of the virulence factors were summarized in this review. J. Med. Invest. 57: 179-182, August, 2010