Conspecific brood parasitism (CBP) is a widespread alternative female reproductive tactic in birds. We monitored CBP and nesting biology of Mandarin Ducks (Aix galericulata) using nest boxes for six breeding seasons in Zuojia, northeast China. CBP occurred commonly (46.2% of completed clutches) during the study and frequency was positively associated with nest densities. The frequency of CBP declined as the nesting season progressed. On average, ∼2.5 females laid eggs in each parasitized nest. There were significant differences in clutch initiation dates and mean laying period between parasitized and un-parasitized nests; no difference was detected for the mean incubation period. Clutch size for un-parasitized nests decreased with advancing initiation date, but not for parasitized nests. The hatching rate for eggs in successful nests was 87.1%, and no significant difference was detected between parasitized and un-parasitized nests. The average number of ducklings that left from successful un-parasitized and parasitized nests was 8.4 and 15.4, respectively. Nest desertion was the main cause for nest failure and sibling trampling was the only cause of duckling loss before departure from nests