Background:Acute diarrhea remains the serious problem in developing countries,especially among children under 5 years of age.Currently,only two or three common diarrhea pathogens were screened at most hospitals in China.The aim of this study was to provide a wide variety of diarrhea pathogens and their antimicrobial resistance patts in children under 5 years of age.Methods:Totally 381 stool samples collected from Tongji Hospital between July 1,2014 and June 30,2015 were tested by culture and/or polymerase chain reaction for eight kinds of bacteria and five kinds of viruses.An antimicrobial sensitivity test was performed using dilution method recommended by the Clinical and Laboratory Standards Institute.Results:Viral infections were mainly identified in infants (0-11 months),whereas bacterial infections were more prevalent in the age of 24-59 months.About 69.8％ of samples were positive for at least one pathogen,51.7％ of samples were virus positive,followed by bacteria positive cases (19.4％),and 12.6％ of cases displayed co-infections with two viruses or a virus and a bacterium.Rotavirus was the most prevalent pathogen,followed closely by norovirus,while Salmonella was the most commonly isolated bacteria,followed by diarrheagenic Escherichia coli (DEC) and Campylobacter.More than 40％ of Salmonella spp.and DEC isolates were resistant to first-line antibiotics (ampicillin,trimethoprim-sulfamethoxazole,and tetracycline).Around 10％ of Salmonella spp.isolates were resistant to ceftriaxone and ciprofloxacin simultaneously.Campylobacter spp.displayed high resistance to ciprofloxacin but kept low resistance to azithromycin and doxycycline.Conclusions:The etiology of acute diarrhea varies in children of different age groups.The high frequency of infection with viruses suggests the urgent demand for new viral vaccine development.Proper use of antibiotics in the treatment of acute diarrhea is crucial due to the high level of antibiotic resistance.