Effects of Si addition on mechanical properties of severely deformed copper by accumulative roll-bonding (ARB) have been investigated. Tensile tests and strain-rate jump tests have been carried out at room temperature. For annealed coarse-grained polycrystals, the difference in yield stress sigma (0.2) between pure copper and a Cu-1.64at.%Si alloy was only about 15 MPa while the difference became 170 MPa after the ARB process by six cycles. The strain-rate sensitivity m of pure copper increased with increasing the number N of the ARB cycles for N a parts per thousand yen 5. However, the increase in m becomes less significant for Cu-Si alloys. These findings have been discussed in terms of thermally activated dislocation processes.