Objective To investigate the changes and seasonal fluctuations in the species composition and densities of mosquitoes in Three Gorges Reservoir Area in Yichang, Hubei province, China. Methods Mosquitoes were captured by electric mosquito-catching trap at fixed times and places and were then identified and counted. Results In the early stage of the construction of Three Gorges Reservoir Area in Yichang, the dominant species of mosquitoes in human houses and livestock pens were Culex pipiens quinquefasciatus, Armigeres subalbatus, Cx. pipiens pallens, and Anopheles sinensis. The dominant species, however, has been Ar. subalbatus in human houses since 2005 and in livestock pens since 2007. The adult mosquito density was significantly lower in human houses than in livestock pens. The seasonal fluctuation in adult mosquito density was in a bimodal pattern, with density peaks in the first ten-days period of June and the first ten-days period of August. Conclusion With the environmental changes in the Three Gorges Reservoir Area in Yichang, the density and species composition of mosquitoes vary. Mosquito monitoring should be strengthened to provide the basis for decision-making basis for effective prevention and control of vector-borne diseases.