Objective To determine the species and density of mosquitoes and their seasonality in the urban areas of Hainan province, China and to provide a technical foundation for controlling mosquito vectors. Methods From January to December 2012, mosquitoes were captured by light-traps at night in the urban areas of 18 cities or counties of Hainan province to determine the species composition and their density. Results A total of 40 448 mosquitoes (10 species, 4 genera) were collected in the urban areas of Hainan; Culex quinquefasciatus Say was the dominant species, accounting for 46.88% of all mosquitoes. The density index of mosquitoes was 1.17-4.86 mosquitoes per light trap per hour, and the mean value was 2.82 mosquitoes per light trap per hour. The seasonalityof mosquitoes was unimodal, and the peakoccurred from April to May. Conclusion The species and density of mosquitoes and their seasonalityin the urban areas of Hainan province were well documented in this stusy, which provides a technical foundation for further systematic monitoring of mosquitoes, control operations, and prevention of mosquito?borne diseases.