To study the epidemic situation and dominant strain of influenza in children with acute respiratory infection (ARI) during Flu season from Oct. 2005 to Mar. 2006 in Taiyuan. METHODS: Madin-darby canine kidney (MDCK) cell culture and hemagglutination inhibition (HI) assay were used to isolate and identify type A influenza viruses (H1N1 and H3N2) and B influenza viruses from clinical samples collected from outpatients who visited the Department of Pediatric because of ARI from Oct. 2005 to Mar. 2006. Oct. 2005 and Mar. 2006, we collected 415 blood samples from children and adults to detect the influenza virus antibody titers by HI test to exclude respiratory diseases. RESULTS: 7 strains of H1N1 were isolated from 87 clinical specimens, with a positive rate of H1N1 as 8.04%. Out of 415 blood samples being collected, the positive rates and the geometric mean titer of H1N1 antibody Mar. 2006 were significantly higher in 0-3, 3-7 and 7-18 year-olds than Oct.2005. CONCLUSION: H1N1 epidemic influenza did occur among children in winter and spring of 2005--2006 in Taiyuan city.