Abstract: Objective To understand the epidemiology of respiratory syncytial virus (RSV) infection in children in Taizhou. Methods RSV antigen was detected in the nasopharyngeal secretions or throat swabs collected from 3556 children with respiratory tract infection from January 2005 to December 2008 by using direct immunofluorescence assay. Results RSV antigen positive rates was 42.23%,20.24%,46.40% and 22.16% respectively during this period. The differences on the positive rate in different years were significant. The disease occurred sporadically all the year round, but the incidence peaked in different time in different year. A total of 1281 of 3556 samples (36.02%) were RSV antigen positive. In children aged 1 years,1081 samples were positive (30.40%), in children aged 1-3 years,174 samples were positive (4.89%), in children aged 3-13 years,26 samples were positive (0.73%), the differences were significant (P0.01). 908 cases were males (35.75%) and 373 were females (36.71%), the difference was significant (P0.05). Conclusion RSV was the main pathogen causing respiratory tract infection in young children during winter and spring in Taizhou, but the infection rate was different in different year, and was higher in younger age group. Both boys and girls were susceptible to RSV infection.