A technique for the determination of the critical current of superconducting thin films by a current‐dependent ac susceptibility measurement has been developed. This method has been used to characterize superconducting YBa2Cu3O7−xfilms growninsituat 1073 K by metalorganic chemical vapor deposition. Two superconducting phases with transition temperatures of 91 and 84 K have been detected by the measurement of ac susceptibility as a function of temperature even though the variation of resistance with temperature indicated a sharp transition. The critical current densities of the two superconducting phases have been determined from the variations of ac susceptibility with current at constant temperature and found to be equal to 1.14×104A/cm2and 3.6×103A/cm2at 75 K. The advantages of the technique in comparison to current methods of measurement of critical current are discussed.