Perovskite-structured transition metal oxides, AMO₃, demonstrate catalytic activities for oxygen evolution reaction (OER), which can be enhanced by chemical substitutions for both A- and M-sites. Considerable efforts are needed to realize the optimum composition with high OER activity because of the huge composition space for doped perovskites of A_1−xA′_xM_1−yM′_yO₃, where A and M ions can be respectively replaced by A′ and M′ ions at arbitrary ratios. Combinatorial synthesis methods were extensively utilized to examine the properties of overall compositions of transition metal oxides. However, perovskite oxides requiring high-temperature treatments were not eligible for the above methods because of the low heat resistance of the conductive substrate, such as indium tin oxide glass and carbon. In this study, we propose an efficient method using the high-temperature synthesis of polycrystalline thin films of perovskite oxides on quartz glasses and Pt films to systematically investigate the OER catalytic activities of perovskite oxides of La_1−xSr_xFe_1−yCo_yO₃ with 100 distinct chemical compositions in 0 ≤ x ≤ 0.9 and 0 ≤ y ≤ 0.9. X-ray diffractometry confirmed that all the samples loaded on the quartz glass crystallized in perovskite structures, whereas the electrochemical study unveiled a continuous landscape depending on both x and y for La_1−xSr_xFe_1−yCo_yO₃. The present method proposes the high-throughput screening for highly active OER perovskite oxide catalysts.