Abstract: Laser cladding of Co-based alloy (C5) and Co-basedalloy with 25 vo1% B₄C (B₄C/Co) on low carbon steel suhstrate has beenobtained by 5 kW CO2 continuous wave laser.The effect of B₄C particleson mierostrueture,mierohardness and wear resistance of Co-based alloycoating is investigated.The results show that microstructures of the two coatings were the dendrites of the sub-euteetic structure.Co55 coating isconsisted of "y-Co and (Cr,Fe)7 C3,and B4C/Co coating is consisted of/-Co,Cr7C3,Cr23C6,Fc23(C,B)6 and CrB2.B4C particles had com-pletely dissolved in the Co-based alloy during the laser cladding.Thedendrites of the B4C/Co coatings were much finer than that of the Co55 coating.Mierohardness and sliding wear resistance of the B₄C/Co coating were higher than that the Co55 coating.The strengthen mechanism of the coatings is analyzed.