In order to explore microstructure and expression of apoptosis-related protiens in Whooper Swan (Cygnus cygnus) kidney, paraffin sections of kidney were observed after H.E staining and expressions of Caspase-3, Bcl-2, Bax, and AQP-3 proteins were examined by immune histochemical methods. The results show that the kidney tissue of Whooper Swan consists of nephrons, collecting ducts and connective tissue. The glomerulus of renal corpuscle was composed of convoluted capillaries. The proximal tubule was lined with simple cuboidal epithelium, with a well-developed brush border. The thin limb and the distal tubule with brushless border respectively consist of simple squamous epithelium and cubic epithelium (Fig. 1a, b). Caspase-3, Bcl-2 and Bax were expressed in the epithelium of the proximal tubule. Caspase-3 was present in the distal tubule. Bcl-2 and AQP-3 were expressed in the collecting ducts. Bcl-2 was expressed occasionally in the endothelium of glomerular capillary (Fig. 1c﹣i). Caspase-3, Bcl-2, Bax and AQP-3 may have an important role in stabilizing the structure of nephron and collecting duct and the regulation of water balance in Whooper Swan kidney.