Purpose This study aims to improve the oxidation resistance of SS304 stainless steel by fabrication of Mn–Co–Ni-coated layer. Mn–Co–Ni coating with the thickness ranging from 1.76 to 8.50 micron were prepared by electroplating process on SS304 stainless steel, focusing on the plating time which play significant roles on the performance of the film thickness and crystallize size. Design/methodology/approach Mn–Co–Ni coating layer was applied on AISI 304 stainless steel using electroplating process with solution consisted of cobalt sulfate (CoSO4), manganese sulfate (MnSO4) and nickel sulfate (NiSO4). Variation of Mn–Co–Ni coating, the morphology of the film and oxidation kinetics were investigated by using scanning electron microscopy and x-ray diffraction analysis. Furthermore, the sample with coating layer was tested by oxidation and Cr evaporation test. Findings From the formation parameter due to plating time for the conversion coating, it was found that plating time plays significant roles in the performance of the coating thickness and crystallize size. The crystallize size has an inverse relation to the full width at half maximum of diffraction peak. Film thickness higher than 6.07 micron causes a decrease in oxidation resistance and an increase of Cr evaporation from SS304 stainless steel. In this study, the Mn–Co–Ni coating with a thickness lower than 3.77 micron showed coating protection of oxidation better than SS304 substrate. Originality/value The effect of coating thickness was investigated to understand the properties of the coating. Furthermore, oxidation and Cr evaporation test were applied to evaluate the oxidation resistance of the coating layer.