Abstract: In order to investigate the mechanism underlying postmortem proteolysis of muscle proteins during meat aging, five broilers were slaughtered and treated individually. After breast muscles were removed, the samples at death were obtained quickly. The other muscles were dissected into small blocks and divided into six groups randomly. One group marinated in solution containing 100 mmol/L NaCl and 2 mmol/L NaN₃ was designated as control, the others were soaked in solutions as controls but containing 30 mmol/L EGTA, 20 mmol/L CaCl₂, protease inhibitor cocktail (10 mL/tablet), 100 μmol/L caspase3 selective inhibitor(DEVD-CHO), 20 mmol/L CaCl₂ plus protease inhibitor cocktail, respectively in the ratio 1∶1(W/V) (meat : solution), then stored at 4℃ for 1, 3, 7 d. At each conditioning time point, meat samples were obtained, and the changes of myofibril proteins (titin, nebulin, desmin, and troponin-T) were examined by SDS-PAGE and western blotting. Results reveal that proteases inhibitor cocktail and DEVD-CHO inhibit myofibril proteins digestion markedly, whereas calcium accelerated the process implying that the endogenous proteases contribute to meat protein degradation, calcium may play a role by activating calpains and that the apoptosis related caspase-3 is possibly another new biological candidate involved in meat tenderization.