Structural features of newly found perovskite-based iron pnictide oxide system have been studied. Compared to REFePnO system, perovskite-based system tend to have smaller Pn–Fe–Pn angle and higher pnictogen height owing to low electronegativity of alkaline earth metal and small repulsive force between pnictogen and oxigen atoms. As–Fe–As angles of (Fe2As2)(Sr4Cr2O6), (Fe2As2)(Sr4V2O6) and (Fe2Pn2)(Sr4MgTiO6) are close to ideal tetrahedron and those pnictogen heights of about 1.40Å are close to NdFeAsO with optimized carrier concentration. These structural features of this system may lead to realization of high-Tc superconductivity in this system.