We report on the study of insulator-to-metal transition in post-perovskite compound CaIrO3. It is discovered that a gradual chemical substitution of calcium by yttrium leads to the onset of strong metallic behavior in this compound. This observation is in stark contrast to BaIrO3, which preserves its Mott insulating behavior despite excess of charge carriers due to yttrium doping. Magnetic measurements reveal that both compounds tend to exhibit magnetic character irrespective of the chemical substitution of Ca or Ba. We analyze these unusual observations in light of recent researches that suggest that CaIrO3 does not necessarily possess j = 1/2 ground state due to structural distortion. The insulator-to-metal transition in CaIrO3 will spur new researches to explore more exotic ground state, including superconductivity, in post-perovskite Mott insulators. 1-5 One recent proposal has suggested the application of 5d iridium oxide compound in the spincurrent detection.6 The ground state in majority of these materials, A 2 IrO 3 and BIrO 3 (where A = alkali metals and B = alkaline earth metals), is often described as a Mott insulting state, where the Ir 4+ ion with a (t 2g ) 5 electronic configuration splits into a fully occupied j = 3/2 state and a half-filled j = 1/2 states. 7-11 While the quantum-mechanical nature of the spin-orbit coupling is considered key to the quantum Hall effect in topological insulating materials, 12 its interaction with cubic crystal field in Ir 5d transition element ensures a j = 1/2 ground state in Mott insulator iridates. 10,13,14 The bandwidth of the j = 1/2 state w N t, where N is the coordination number and t is the Ir-Ir hopping matrix, is found to be comparable to the Coulomb repulsion potential U in BIrO 3 ; thus on the verge of attaining the metallic character.15 A simple modification in the structural properties or, the change in the hopping integral achieved via higher carrier density can, therefore, induce a highly desirable metallic behavior in iridium oxide compounds of 1-1-3 phase.In this letter, we present new results on the presence (absence) of insulator-to-metal transition in the holedoped CaIrO 3 (BaIrO 3 ). In a novel observation, it is found that the yttrium substitution of calcium leads to an onset of metallic behavior at x = 0.4 in Y x Ca 1−x IrO 3 , which is not the case in Y x Ba 1−x IrO 3 . Both compounds, however, preserve magnetic characteristic irrespective of the chemical doping. In another notable observation, the dimensionality analysis of the electrical transport data below the magnetic transition demonstrates a quasi-2D electronic pattern (d = 2.4) in CaIrO 3 , which is in stark contrast to 3D electronic transport in BaIrO 3 . CaIrO 3 and BaIrO 3 manifest Mott insulating behavior with charge gap of 0.17 eV and 50 meV, respectively. 11,16 While CaIrO 3 crystallizes primarily in the orthorombic phase of crystallographic group Cmcm (similar to MgSiO 3 ),17 BaIrO 3 forms a monoclinic structure (C2/m).9 In both compounds, the chemical structure is composed of...