HGganAas Co based alloy coatings have been produced by using a 5 kW CO 2 laser with wide/narrow band beam on Ni based superalloy/45 # steel. Cross-section or vertical-section of such coatings have been examined to reveal their microstructure using phase-contrast microscope, scanning electronic microscope and X-ray diffraction instrument. The results showed the primary phase γ-Co dendrite and γ-Co+Cr 23C 6 eutectic Co-existed in the coating. Dendrite grew perpendicularly to the interface in wide band laser beam coatings and more direction in narrow band laser coatings because of heat flux. There was a white thin layer of planar crystallizing at the interface of 45 # steel substrate, and the width of the broad beam coatings was wider than that of narrow beam coatings. It was irregular and no sign of white thin layer at interface region of Ni-based alloy substrate. The results also showed that dendrite grew paralleling to laser scanning direction near top surface of the central line coatings (vertical section).