This study aims to identify the pathogens of diarrhea in Vientiane Capital, Lao People’s Democratic Republic (Lao PDR). The data of 2482 patients who visited eight health facilities due to diarrhea in 2012-2015 were retrospectively reviewed. Stool or rectal swabs collected from all patients were tested for bacteria. Children who were under 5 years old were additionally tested for rotavirus. Of 2482 cases, 1566 cases were under 5 years old, and at least one enteropathogen was detected in 475 cases (19.1%). Salmonella species was the most commonly detected bacterial pathogen. Enteropathogenic Escherichia coli (EPEC) and Salmonella species was the major pathogen in the dry season and the wet season, respectively. Eighty-seven patients tested positive for multiple bacteria. Rotavirus was detected in 291 children under 5 years old (32.4%), mostly from October to April. The major bacteria of coinfection with rotavirus were EPEC followed by Salmonella species. Salmonella species was the predominant bacterial pathogen of diarrhea of all ages, and rotavirus was the predominant pathogen among children under 5 years old. Further studies examining other types of pathogens for diarrhea and the introduction of a rotavirus vaccine for children are needed in Lao PDR.