This article compares the creep rupture responses of aluminide coated samples with uncoated ones to elucidate the effect of diffusion layers on resistance against creep. Three Ni-base single crystal superalloys, CMSX-4, TMS-75 and TMS-138, were chosen for present study. Creep specimens had thicknesses ranged from 1 mm to 4 mm to simulate the varying dimensions across the actual turbine blade. Creep conditions were set at 1060°C-137 MPa and 1100°C-137 MPa. Experimental results indicated that the creep-rupture lives of coated specimens were shorter than those of the bare samples. In particular, the coated TMS-138 specimen with 1 mm thickness had an 86% reduction in creep rupture life. Microstructural observations on coated samples indicated the formation of diffusion zones beneath the coating; a creep life model was then developed to taken account the reduction in load bearing cross sectional area. In conclusions, the creep-rupture lives predicted by the model have shown good agreement with the experimental values.