Abstract: Objective this assay was desired tO explore the epidemic characteristics of the outbreak of dengue fever in Zhejiang province in 2004 and to provide a scientific basis for the prevention and control measures．Methods A retrospective epidemiological investigation study was conducted to search the patients by given definition．IFA were used for detecting the and-dengue virus antibodies，and the serum samples were collected from the patients in acute stage for dengue virus isolation with C6/36 cell and the positive samples were identified by RT-PCR．The mosquito larvae density at epidemic spot was measured with BI．Results The period of epidemic caused by type I dengue virus was 85 day．Patients were localized in one town．Gender distribution was male of 29 and female of 54．And age distribution was localized in 20 to 60 years old with the minimum of 7 and the maximum of 76．The BI in epidemic district reached 326 during the epidemic period．Conclusion The outbreak Was caused by dengue virus type I．The first case was imported from Thailand．Diagnostic errors，delaying insulation Was the major reason leading to the outbreak．Eliminating mosquito is the effective method to control and prevent dengue fever．