Erosion properties of high purity alumina (Al2O3) and yttria (Y2O3) coatings prepared by plasma spraying have been investigated against process plasma in semiconductor and liquid-crystal-display (LCD) production equipments for dry etching. Studies on plasma power dependency have revealed that yttria coatings have showed higher anti-plasma erosion resistance than alumina coating as well as sintered alumina bulk at every condition. Although yttria coatings are inferior to sintered yttria bulk, the difference of the resistance becomes smaller with increasing plasma power. This result positively promotes the application of the yttria spray coating because of increasing plasma power in actual process. Erosion properties of the coatings against Ar/CF4/O2 plasma, whose composition is increasingly being used in commercial process, are also investigated where physical etching effect becomes stronger than the typical CF4/O2 case. It has been found that order of durability (yttria bulk > yttria coatings > alumina bulk > alumina coating) is independent of the gas species used in this study. The mechanism of the plasma erosion is discussed through micro-structural analysis of the eroded surfaces.