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We performed AC quench current tests of AC superconducting multifilamentary NbTi and Nb/sub 3/Sn wires in AC external field by changing the phase difference between the transport current and the external field. The Nb/sub 3/Sn AC wire was more stable than the NbTi wire and the peak value of the AC quench currents reached to the levels of the DC quench current while the quench current of the NbTi wire was much less than the DC quench current. The data also showed strong dependence of the quench currents on the phase difference. We made a theoretical model to analyze the stability of AC wire assuming that the instability was caused by the magnetic instability due to the transport currents. In the analysis, the wire temperature was numerically evaluated by calculating instantaneous AC losses and solving the thermal equilibrium equation. The quench current was estimated. In the paper, the experimental results are compared with theoretical ones and it is shown that the theoretical model explains AC quench behaviors of the wire subject to the external AC magnetic field.