We investigated breeding biology on two populations of Common Coots (Fulica atra) in Anbanghe Wetland and Longfeng Wetland, Heilongjiang Province, China, in 2008 and 2009 and found out that conspecific brood parasitism was common in the two populations. The proportion of parasite nests was 38.55% on average in the two populations. Egg recognition and rejection was a particularly defense taken by the hosts parasitized by the neighbors or floaters, egg buried and ejection as well as piped were the common manners of parasite defense. The nearest distance between parasite nests was 41.906±4.035 m (n=32) which is smaller than nearest distance (51.765±4.532 m, n=51) between un-parasite nests. However, the difference was not significant (t=-1.503,df=81,P=0.137). It seems the territory behaviors of F.atra in breeding season play a role in the conspecific parasitism, which has been hypothesized and needed to be tested in the future study.