Abstract: Objective To understand the epidemiological and etiological characteristics of an outbreak of acute respiratory tract infection in Gansu province. Methods Descriptive epidemiological survey was conducted to describe the epidemiological characteristics of the disease and 118 swabs were collected from the cases for real-time PCR detections of 12 possible pathogens, including influenza A and B viruses, respiratory syncytial virus (RSV), human adenoviruses (HAdVs). Virus isolation was conducted for the samples which were positive in HAdVs detection and the isolated strains were sequenced for Hexon fragment, and the nucleotide sequence was analyzed with software ClustalⅩ and Mega 6.0. Results From 20 December 2014 to 2 February 2015, a total of 118 infection cases were reported, all the cases were children aged 2 months to 11 years. The cases were distributed in 17 of 21 townships of Kangxian, including 27 cases in age group1 year, 40 cases in age group 2-5 years and 14 cases in age group 5 years. Sixty seven cases occurred in boys and 51 cases occurred in girls (1.31:1). The main symptoms included fever, cough and sore throat, and some cases had quinsy and diarrhea. Thirty three HAdV infection cases were laboratory confirmed, which were distributed in 13 townships. Real-time PCR indicated that 33 cases were HAdV7 infections, 7 cases were influenza A(H3N2), 6 cases were RSV infections and 2 cases were co-infected with HAdV and RSV. Eighteen strains of HAdV were isolated by using Hep-2 cells, in which 17 were confirmed by China CDC. One strain of HAdV1 was isolated. The sequencing analysis showed that all the HAdV7 strains, sharing 100% homology, were on the same branch. Conclusion The acute respiratory tract infection epidemic in children was mainly caused by HAdV7, but by influenza A (H3N2) virus in early stage and RSV in late stage. Bad climate, poor management of fever cases, poor ventilation and crowding in hospitals were the risk factors for the outbreak.