Nonreciprocal microwave devices, such as circulators and isolators, play several critical roles in superconducting quantum processors. They route readout signals in a directional manner, protect the quantum system against noise coming from the output chain, and enable reflection measurements by separating input from output. However, the reliance of these devices, on magnetic materials and strong magnets for breaking reciprocity, makes them disadvantageous in scalable superconducting architectures. In this work, we realize and measure an on-chip Josephson isolator, which is formed by coupling two nondegenerate Josephson mixers in an interferometric scheme. Isolation is created, in the active device, by operating the two mixers in frequency conversion mode using balanced, same-frequency microwave pumps, whose phase difference is \pi/2. The applied pumps are generated using an on-chip quadrature hybrid, which equally splits the single pump feeding the device and imposes the required phase difference between the split drives.