Adhesives are widely used in industrial world. However, it is difficult to characterize their mechanical properties because those strongly depend on environmental and mechanical conditions such as temperature, humidity or strain rate. In this paper, we focus on the strain rate dependence of the interfacial strength and investigate the interfacial strength by peel tests under several peel rates. The results show that, in low rate case (under 10-2 mm/s), the interfacial strength was constant and, in middle rate case (10-2 to 103 mm/s), the interfacial strength increased with the peel rate. Over 103 mm/s case, the interfacial strength became lower than those in middle rate cases. From the observation of peeling front by a high speed video camera, the deformation behavior of adhesives changed with the peel rate.