Because of their low cost and Earth-abundant characteristics, materials based on 3d transition metals have attracted great research interest and are considered as promising electrocatalysts for the oxygen evolution reaction (OER), besides the commercial noble metal-based materials, in recent years. In order to improve electrocatalytic activity, it is necessary to design the structures and compositions of electrocatalysts. In this study, a series of multi-shelled CoxNi1-x oxide/phosphide hollow spheres with tunable element ratios were prepared. The electrocatalytic activity of the multi-shelled CoxNi1-x oxide/phosphide is strongly dependent on the molar ratio of Co and Ni. Based on the combined advantages of complex structures and compositions, the multi-shelled Co0.5Ni0.5 oxide/phosphide displays outstanding electrocatalytic performance in terms of high activity and stable durability for the OER, surpassing those of RuO2 and multi-shelled CoxNi1-x oxide/phosphide with other element ratios of Co and Ni. This result suggests a great possibility of rationally designing the composition for highly efficient electrocatalysts.