Objective To investigate the mosquito abundance and their relative species composition within and outside the Rare Birds National Nature Reserve of Yancheng,Jiangsu Province. Methods Sampling was carried out between May and Oct. 2004 at two weeks interval in two foci (the Reserve and nearby residential district) in Sheyang County. Mosquitoes were collected with the modified CDC light trap. Density was calculated,and species were identified. Environmental temperatures,rainfall and relative humidity were monitored during the study. Results A total of 40 912 mosquitoes were captured in the two foci. The sampled mosquitoes were identified as 4 species belonging to three genera (Anopheles sinensis,Culex pipiens pallens,Cx. tritaeniorhynchus,and Armigeres subalbatus). The most abundant mosquito species was An. sinensis and Cx pipiens pallens,which accounted for 97.7% of the whole number. 92% and 8% of the total amount of mosquitoes were collected from the nature reserve and residential district respectively. The most abundant species in the nature reserve and residential district was An. sinensis(60.6%) and Cx. pipiens pallens(76%),respectively. Within the nature reserve,there were two peaks occurred in adult abundance,in mid-and late July and mid-Sept. The abundance of mosquitoes in the area was positively correlated to the temperature (r=0.765,P=0.005). Conclusion The wetland is an ideal breeding place for An. sinensis and Cx pipiens pallens. The peaks of mosquito abundance are in mid-and late July and mid-Sept. It is of importance to carry out surveillance on mosquito vectors with pathogen-transmitting potential.