This study was conducted to evaluate the effect of postmortem aging on pH, temperature, drip loss, sarcomere length, myofibrillar fragmentation index (MFI), myofibrillar protein solubility, released calcium and myofibrillar adenosinetriphosphatase (ATPase) activity in longissimus dorsi (LD), biceps femoris (BF), semimembranosus (SM) and semitendinosus (ST) muscles of goat maintained at 5C up to 20 days postmortem. The results showed that the rates of pH decline, temperature and sarcomere length decreased during aging. There was a significant increase in drip loss of LD, BF, SM and ST at 3, 6 and 9 days, respectively. The increased MFI followed a pattern of LD > ST > BF > SM at 20 days postmortem. The myofibrillar ATPase activity rapidly decreased between 0.1 and 0.2 M ionic strength in all the muscles. The biochemical index of myofibrillar aging (BIMA) value of LD, BF and SM muscles was constant after 9 days postmortem. The results obtained here describe a close relationship between rate of pH decline, decreased sarcomere length and increased MFI and BIMA value during postmortem aging. Therefore, the biochemical indices described in this article could be used as indicators of the degree of aging of the goat myofibrillar structure.