Developing efficient electrocatalysts for oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) are vital to the new generation of electrochemical storage and conversion devices such as electrolyzer, metal-air batteries, and fuel cells. For the demand of reversible fuel cells and rechargeable metal-air batteries, the bifunctional catalyst that can be used for both ORR and OER is gathering attention. In order to address the longstanding problems with high cost and poor stability of noble metal electrocatalysts, perovskite (ABO₃ formula, where A is rare-earth or alkaline metal and B is transition metal) with low cost, high versatility in structure and potential as bifunctional catalyst is of special interest. Applying our successful and novel polymer-assisted chemical solution (PACS) method, we will present the controlled synthesis of (La_0.8Sr_0.2)_x(Mn_1-yB_y)O₃ (B: Ir and Co, x=0-0.1, y=0-0.2) nanoparticles with different particle sizes, A-site nonstoichiometry, B-site doping, and oxygen vacancy, and epitaxial thin films with different crystal orientations. Stuctural characterizations and electrochemical analysis are utilized to investigate the correlation between their compositions, structures, and electrochemical properties.