Abstract: Objective To explore the characteristics and the changes of the dominant strains of influenza in Wuxi, to provide scientific basis for the prevention of influenza. Methods Data of influenza - like illness ILI from monitoring sites in outpatients and the outbreaks of influenza irt year 2005 - 2008 were analyzed. Results From October 2005 to March 2008, there were 37 998 cases ofILI, which on average accounted for 3.67% of all the OPD patients. A total of 1 796 samples were collected, and 395 strains were identified for influenza virus with an average isolation rate of 21.99%. There were three peaks which occurred in December 2005, March 2006 and July 2007 respectively, and in these periods the number of ILI cases, the ratio of ILI in all outpatient visits and the isolation rates were higher than those in other periods. During the three high peak periods, the dominant strains changed accordantly. The percentage of ILI cases under 14 years was 91.03%. The main influenza outbreak place were schools. Conclusion Three peaks of influenza were shown in Wuxi from year 2005 to 2008. The influenza virus has tendency of switchover to dominant strain. Vaccination as the leading in comprehensive measures should be taken to prevent influenza before the peak came especially in those key sites such as schools.