The present study was conducted to evaluate the extent of postmortem proteolysis in longissimus dorsi, biceps femoris, semimembranosus and semitendinosus goat muscles on postmortem aging at an ambient (27C) temperature. The activities of calpains and calpastatin were determined after separation on a (diethylamino)ethyl–Sephacel column (Sigma, St. Louis, MO) and cathepsin (B, B + L and H) by carboxymethyl–Sepharose column (Sigma). The results showed that the decrease in calpain I and calpastatin activities was significantly higher than that of calpain II. Cathepsin B, B + L, H and cystatin were found to fall by 30–80% after 12 h, whereas cathepsin D decreased significantly in all the muscles. The disappearance of titin 1 and nebulin, and the appearance of a 30-kDa component were confirmed by Western blot analysis. The appearance of the 30-kDa component reported here explains the time-induced structural changes of myofibrils. The Z-line degradation had occurred by 6 h postmortem. Cathepsins are not stable compared to calpains during postmortem aging, and both enzymes may play a significant role in the proteolysis of myofibrillar proteins at ambient temperature.