AbstractWe studied the species diversity of water birds in Yueqing Bay in 1997, 1999 and 2003. We observed 54 species of water birds, belonging to 24 genera, seven families and four orders. Number of species and individuals, species diversity index and evenness, and proportion of wader birds decreased from baymouth to bay-head, and was lowest in midbay. The factors affecting bird distribution and diversity were beach width, hydrodynamic conditions and the size of effective upshore intertidal area. In the Yueqing Bay, individual number of water birds tended to decrease year by year，except for those in bay-head, which increased in 2003 over 1999. The decreases between years were insignificant with the exception of baymouth from 1997 to 2003. The decline of bird species diversity and evenness index in Yueqing Bay indicated that the habitats of water birds were being degraded, which might be related to human disturbance such as reclamation.