Authors have studied on plasma spraying of zircon (ZrSiO₄) as one of candidates for an environmental barrier coating (EBC) application, and had reported that substrate temperature is one of the most important factors to obtain crack-free and highly-adhesive coating. In this study, the effect of the yttria addition to zircon on the structure and properties of the coatings were evaluated in order to improve the stability of the zircon coating structure at elevated temperature. The coatings obtained by spraying the yttria added zircon were composed of yttria stabilized zirconia, amorphous silica and yttrium silicate, while the one from monolithic zircon was composed of amorphous silica and tetragonal zirconia high temperature phase. After the heat treatment over 1473K, silica and zirconia formed zircon in all the coatings, however, the more the addition of yttria was, the less amount of zircon were formed; which resulted in the less porosity of the coating at elevated temperature. Yttria added zircon coatings showed also good adhesion even after the heat treatment up to 1000h, while monolithic zircon coating had peeled off.