The microstructures and the creep behavior of ZK31+4Si magnesium alloy processed by Equal channel angular pressing (ECAP) were investigated. The experimental results show that the coarse Chinese script-like Mg2Si precipitates are refined to fine polygonal shape particles and redistributed dispersedly after ECAP. The creep resistance is greatly enhanced after ECAP. The ctable creep rate of the 8-pass ECAPed specimen is nearly 1/15 of that of the as-cast one, and its creep life is increased by about 8 times. The curves of the minimum strain rate versus the stress show that the alloy ECAPed either through 8 passes or through 4 passes exhibit a same stress exponent n?4. Furthermore, the theoretical calculation results according to the dislocation creep model with n=4 are well in agreement with the experimental values, indicating that the creep under the present test condition is controlled by the movement of dislocations.