Abstract: Objective To investigate the prevalence of human bocavirus(HBoV) in infants and young children with acute respiratory tract infection(ARTI) and to identify molecular character of the virus.Methods Nasopharyngeal aspirates were taken from 202 hospitalized pediatric patients from September 2008 to May 2009,and the NP1 gene fragments of HBoV were detected with PCR amplification.VP1/VP2 genes were sequenced to analyze the variation character and to construct phylogenetic tree.All HBoV-positive samples were examined with multi-PCR for other 12 respiratory viruses and PCR for WU polyomavirus.Results Of 202 pediatric patients,14(6.9%) were positive for HBoV.The age group with the highest infection rate was 6-12 months with an infection rate of 14.3%(6/42).All HBoV-positive children were subjected to pneumonia and asthmatic bronchitis; 85.7%(12/14) of HBoV-positive patients were co-infected with other respiratory viruses,and among them,58.3%(7/12) were 3 or more viruses co-infection.Totally 13 HBoV VP1/VP2 genes were successfully sequenced and phylogenetic analyses showed that they were all belong to Ib cluster.Nucleic acid and amino acid identity was 99.0%-99.8% and 99.0%-99.9%,respectively,compared with group I strains which were downloaded from GenBank.Conclusion HBoV was prevalent in young children less than 6 years old in Tianjin.Co-infection of HBoV with other respiratory viruses was common.All HBoV prevalent in Tianjin belongs to Ib cluster.