Proteolytic activity of the tissue extracts from the muscle of mackerel, Scomber japonicus, and sardine, Sardinops melanostcta, was comparence with referenced to the optimum reaction condition. Thermal stability and change of proteolytic activity of the tissue extracts during storage were investigated. The existence of acid, weak acid and alkaline proteinase was identified in the ordinary and dark muscle of the mackerel and sardine. Specific activity of acid proteinase was stronger than weak acid or alkaline proteinase in the both fish. The proteolytic activity of the tissue extracts on the optimum reaction condition was: ordinary muscle of mackerel, 0.12 nM-Tyr. eq./mg-prot. /min. at pH 3.0 and $50^{circ}C$; dark muscle of mackerel, 0.36 nM-Tyr. eq./mg-prot. /min. at pH 3.0 and $45^{circ}C$; ordinary muscle of sardine, 0.45 nM-Tyr. eq./mg-prot. /min. at pH 2.4 and $45^{circ}C$; dark muscle of sardine, 0.24 nM-Tyr. eq./mg-port. /min. at pH 2.4 and $45^{circ}C$. The proteinases distributed in the muscle of mackerel and sardine were stable with the heat treatment at $45^{circ}C$ for 5 minutes, but those in the dark muscle of mackerel was stable with the treatment at $5^{circ}C$ for 5 minutes. The proteinases from the muscle were slowly inactivated with the whole storage days at $5^{circ}C;and;-15^{circ}C$, those were more stable at $-15^{circ}C;than;5^{circ}C$ storage.