Objective To analyze the epidemiological characteristics of dengue fever outbreak in Shaoxing City,and to provide a scientific basis for the prevention and control.Methods A retrospective epidemiological investigation was conducted to search the patients by given definition.Enzyme linked immunosorbent assay (ELISA)was used for detecting the anti -dengue virus antibodies.The serum samples from patients were collected for dengue virus isolation and the positive samples were identified by RT -PCR.Breteau Index was carried out to monitor the density of mosquito larva. Results A total of 42 cases were found with no death reported.The symptoms mainly included fever (1 00%),fatigue (59. 52%),arthralgia(50. 00%),headache (47. 62%)and rash (38. 1 0%).The outbreak lasted for 71 days with the first case occurred in July 1 5 and the last in September 23.The peak was from August 30 to September 5. Thirty seven cases were located in Keqiao District and 5 cases were in Yuecheng District.The male/female ratio was 1 . 33∶1 .The age of cases ranged from 1 0 to 79 years old with the 40 -(1 9. 05%)and 50 -(1 9. 05%)age group making the largest proportion.The outbreak also showed family aggregation.IgM antibody and nucleic acid of dengue virus were detected from serum samples of 1 2 patients.The sequence of the isolation indicated that this outbreak was caused by dengue virus typeⅡ.Conclusion The imported cases,high density of mosquito vector and missed diagnosis might contribute to this outbreak.Developing a practical scheme for mosquito elimination,improving diagnostic capacity of medical staff and their consciousness of reporting could be important ways to control dengue fever.