The interface morphologies of single crystal superalloy CMSX-2 have been studied over a range of cooling rate with large variations in withdrawal speeds in directional solidification. A superfine cellular structure was obtained under both high thermal gradient up to 1000K/cm and fast withdrawal rate up to 1mm/sec. The high rate directional solidification results in reduction in primary and secondary dendrite arm spacing, refinement of λ’ phase, reduced microsegregation of alloying elements and smaller size of γ-γ’ eutectics. Rupture life and plasticity of fine structure samples at 1323K increase significantly than that in conventional directional solidification process.