All cases of antibiotic-associated diarrhea from all infected patients of 2006 in our hospital were investigated retrospectively.There were forty-two AAD cases in 2006 and it was 13.86% in all nosocomial infected cases.Six cases died of AAD and the mortality was 14.29% in the patients with AAD.It was 15.79% in all death cases from nosocomial infection.Antibiotic-associated diarrhea,especially pseudomembranous colitis,affects seriously health and life and it has been becoming a severe question.The key of preventing antibiotic-associated diarrhea is reasonable usage of antibiotics.Microecological modulators can effectively prevent and treat antibiotic-associated diarrhea.