Josephson junctions were fabricated at the interface of YBa2Cu3O7−x(YBCO) and Nd1.85Ce0.15CuO4−y(NCCO) in heteroepitaxially grown superconducting bilayers. Devices of various configurations and sizes were fabricated, and they display a resistively shunted junction likeI–Vcharacteristics with hysteresis at low temperatures. A clear ac Josephson effect was observed under microwave irradiation, and critical currents were completely suppressible by external magnetic fields. Oxygen diffusion or charge diffusion at the interface are possible origins for the barrier formation. ©1995 American Institute of Physics.