Abstract: The effects of Ta on the solidification microstructure of the Re-containing hot corrosion resistant Ni-base single crystal were investigated. Results showed that Ta addition significantly modified the solidification behavior and further influenced the as-cast microstructure. Ta addition changed the solidification characteristic temperatures and decreased the segregation of refractory elements (Re and W) as well as increased the solidification temperature range from 39.0 to 61.8℃ as Ta addition increased from 2wt% to 8wt%. The integration of these two factors increased the primary dendrite arm spacing and changed the morphology and size of γ' precipitates. With increasing Ta addition from 2wt% to 8wt%, the size of γ' precipitates in the dendrite core increased substantially from 0.24 to 0.40 μm, whereas the γ' precipitates in the interdendritic region decreased slightly from 0.56 to 0.47 μm. This paper then discussed the mechanism of these "Ta effects".