A catalyst for ozone decomposition which comprises: at least one oxide of a metal selected from the group consisting of Cu, Mn, Co, Fe and Ni; and at least one oxide of a metal selected from the group consisting of Ti and Ag, and/or Au.A further catalyst freed from deterioration in activity even when it is used under severe conditions, which comprises: a ternary metal oxide represented by the formula of xMnO.sub.z.yAg.sub.z O.zTiO.sub.z wherein weight proportion coordinates (x, y, z) of the oxide on a triangular diagram are either on sides of a triangle formed by connecting three points (20, 10, 70), (80, 10, 10) and (20, 70, 10) with straight lines or within the traingle, as seen in FIG. 1.