The penetration phenomena of liquid Mn into porous ZrO2-8 wt.% Y2O3 coating, plasma sprayed on JIS SS400 steel substrate was studied by heating at 1573 K in a vacuum atmosphere, and the possibility of improving the mechanical properties of the coating by heat treatment with liquid Mn was examined. It was found that liquid Mn rapidly penetrated the coating and formed an interface between the coating and the substrate. The densification of the coating occurred when ZrO2 particles were sintered with liquid Mn that penetrated the porous ZrO2 coating. It was revealed that the dense coating was free of porosities and that its hardness increased greatly after heat treatment with Mn, compared with as-sprayed ZrO2 coating. Moreover the modulus of elasticity and the fracture toughness of the coating reached the same levels as those of sintered partially stabilized ZrO2 (Y2O3).