A case of a 5-year-old boy who fulfilled all the criteria for Kawasaki disease (KD) was described. He had associated bilateral coronary artery aneurysms. Our study revealed the isolation of Yersinia pseudotuberculosis in stool cultures, and the elevation and seroconversion of the agglutination antibody titres, and hence he was diagnosed as Y. pseudotuberculosis infection-positive. We also demonstrated the positive mitogenic activity of the culture supernatant of the isolated bacterium from the patient and detected Y. pseudotuberculosis-derived mitogen by PCR. This case therefore suggests that Y. pseudotuberculosis might be closely related to the cause of KD.