The recent study on active amorphous catalytic materials provokes rethinking of the previous research on atomic and electronic structures in the crystalline catalyst. Is there any active catalyst with biphasic structure, in particular the integration of crystalline and amorphous components? Inspired by this question, a crystalline–amorphous biphasic quaternary oxide catalyst is novelly fabricated via one-step solvothermal method in this work. The as-prepared catalyst displays a well-designed core-shell architecture composed of crystalline Co(ZnxNi2-x)O4 nanorod (core) and amorphous NiO nanosheet (shell). This heterogeneous core-shell catalyst exhibited high activity in the oxygen evolution reaction by demonstrating a low over-potential of 1.57 V vs RHE, a high half-wave potential (0.89 V vs RHE), and long-term electrochemical stability for 25 h. It was found that the synergistic effects from the amorphization of the shell on the one hand, and the atomic/electronic structure of the crystalline core on the other hand, could significantly facilitate the catalytic activity both at the surface and in the bulk volume of the solid oxides. Therefore, this new developed crystalline-amorphous biphasic catalyst could provide instructive roles in the future design of new catalysts for O2 evolution and other catalytic reactions.