New Ir(VI) and Ir(V) containing perovskites oxides of the type, BaM0.5Ir0.5O2.75 and BaM0.25Ir0.75O3 (M = Na or Li) have been synthesized under high oxygen pressure conditions using the thermal decomposition of KClO3 in a belt apparatus. These materials have been characterized by X-ray diffraction, iodometric titration, and magnetic susceptibility measurements. BaM0.25Ir0.75O3 (M = Na,Li) phases do not show 1:3 type ordering of M and Ir cations at the octahedral sites of the perovskite structure. The physico-chemical characterization of the prepared iridium perovskites show that the structure depends on synthetic conditions employed, the oxidation state of iridium and the coordination of Ir(n+) (n = 5, 6). The ionic radii of the counter cations, M (Na or Li), also play an important role in the stabilization of a particular structure by altering the tolerance factor.