The microstructure, the segregation and the evolution of g/g ′ eutectic during the solidi?cation of Ni-base superalloy DD6 prepared by dual heating zone melting and liquid-metal cooling (LMC) direction solidification technique were investigated over a range of cooling rates. The microsegregation behavior during solidi?cation was also quantitatively examined by EPMA to clarify the in?uence of elemental segregation on the evolution of g/g ′ eutectic. The effect of dendrite arm spacing was also taken into consideration. The results demonstrate that the g/g ′ eutectic fraction first increases and then decreases with the increasing of cooling rate. The back-diffusion in solid phase would reduce the microsegregation during dendrite growth. Back-diffusion occurs during the solidi?cation of Ni-based single crystal superalloy DD6, but its influence on decreasing of the volume fraction of g/g ′ eutectic would be negligible depending on the diffusivity of each solute element when the cooling rate is up to a certain limit. As the cooling rate increases, the dilution effect of microsegregation owing to dendrite arm spacing decrease plays a leading role during solidi?cation