Objective To investigate the expression of calpains and calpastatin in diaphragm of a rat model of chronic obstructive pulmonary disease(COPD). Methods Fotry male Wistar rats were randomly divided into the control group and the COPD group. Rats in the COPD group were copied by expo -sing to cigarettes smoking and dripping lipopolysaccharide into trachea. Pathological changes of lung and diaphragm were deteted. Immunohis-tochemistry and RT-PCR were performed to determine protein and mRNA expression of calapins and calpastatin. Results Diaphragmatic atrophy was observed in rats in the COPD group instead of the control group. The protein and mRNA expression of calpains in diaphrag-m of COPD group were Increased than those in the control group(P < 0.05). On the contrary ,the expression of calpastatin was significantly reduced in rats in the COPD group(t =-9.38 and-2.97;P < 0.001 ,P = 0.005). Conclusions An imbalance in the expression of calpains/calpastatin in diaphragm was observed in COPD rats ,and this imbalance may be responsible for diaphragm atrophy.