The effect of laser power outputs on microstructural evolution of cobalt (Co) treated by laser surface melting (LSM) are systematically characterized by electron channeling contrast and electron backscatter diffraction techniques equipped in scanning electron microscope.Results shows three distinctly different microstructural characteristics from surface to substrate in Co samples treated by LSM:solidification substructure (cell and cellular-dendritic) and phase transformation structure (ε martensitic plates) in the elongated columnar grains for melting zone (MZ),ε martensitic plates in insufficient recrystallization grains for heat affected zone (HAZ),and fully recrystallization microstructure for base metal (BM).Although the similarity of general evolution profiles for LSM treatment on Co under different laser power outputs,the trend of the penetration and width depth for MZ is obviously increased with increase of laser power outputs,and cellular substructure is more pronounced in the specimens treated by the higher power.The metallurgical mechanisms for LSM treatment of Co,which are closely related to the interaction between heat sources and metal,are systematically discussed in this paper.