AC losses of HTS pancake coil for the superconducting fault current limiter were investigated. The measured AC losses of pancake coil were found to be primarily heat generation by vibration. Therefore, the rigidity of coil was improved by epoxy impregnation, resulting in a 50% reduction in AC losses. Therefore, the total AC losses of HTS pancake coil are dependent on the rigidity of coil. In the present paper, the relationship between resonance frequency and heat generation by vibration is shown.