A prospective survey was made on acute diarrhea in rural Yizu minority children under 5 years of age in Lunan County, Yunnan Province between 1986-1987. Through the investigation of 2 years of 1016 children under 5 years of age, the incidence of acute diarrhea was 1.43?0.07 times per child—year. The highest incidence rate was in the childen aged 0.5—1 year. The epidemic season was from April to June, but the cases occurred all the year round. ETEC was the most frequently identified pathogen (39.1%) and rotavirus the second (26%). The main risk factor of the acute diarrhea was drinking pond and ditch water.