The rate controlling mechanism for creep deformation of the single crystal Ni-based superalloy, CMSX-4, at 1073-1273K and 250-700MPa was investigated. Constant load tensile creep tests and creep interrupted tests up to the minimum creep stage, were conducted in air. And TEM observations carried out on creep interrupted specimens. Stacking faults in the ’ were observed on creep interrupted specimens at the temperature lower than 1223K and the stress higher than 500MPa. The number of stacking faults increases monotonously with a decrease in temperature, and remarkably with an increase in stress. The stacking fault formation depends on creep temperature and stress conditions. The stress exponent of minimum creep rate, n value, and the activation energy for creep, Qc, were constant for all creep test condition range. From these results, the stacking fault formation has no influence on creep resistance and the rate controlling mechanism for creep deformation at the low temperature and high stress condition was not thought to be shearing the ’, but movement of the mobile dislocations in the channel as well as at the high temperature and low stress condition.