In May 1986, an outbreak of epidemic acute diarrhea occurred in one city and three counties in Yanbian area. The diarrheal cases were seen in all age groups, the majority of the cases were seen in adult age group. No bacterial pathogens were isolated in 22 fecal samples examined, however rotavirus like particles of 52-68 nm in diameter were found in 50% (11/22) of fecal samples by the immunoelectron microscopy using convalescent sera. Examination by the adult diarrhea rotavirus (ADRV) ELISA kit showed positive reaction in 86% (6/7) of fecal extracts, however in all 22 fecal extracts examination using ELISA kit for detection of group A rotavirus showed negative reaction. The PAGE patterns of viral RNAs similar to those of ADRV were seen in 13 out of 22 fecal extracts. The detection rate by PAGE analysis was 59%. Based on the above data, the etiological agent of the epidemic acute diarrhea, which occurred in Yanbian area, was identified to be ADRV.