The volume of the lesions created by conventional single-frequency high-intensity focused ultrasound (HIFU) is small, which leads to long treatment duration in patients who are undergoing tumor ablation. In this study, the lesions induced by confocal dual-frequency HIFU in an optically transparent tissue-mimicking phantom were investigated and compared with the lesions created by conventional single-frequency HIFU. The results show that using different exposure times resulted in lesions of different sizes in both dual-frequency and single-frequency HIFU modes at the same spatially averaged intensity level (ISAL = 4900 W cm(-2)), but the lesion dimensions made in dual-frequency mode were significantly larger than those made in single-frequency mode. Difference frequency acoustic fields that exist in the confocal region of dual-frequency HIFU may be the reason for the enlargement of the lesions' dimensions. The dual-frequency HIFU mode may represent a new technique to improve the ablation efficiency of HIFU. The total time for the ablation of a tumor can be reduced, thus requiring less therapy time and reducing possible patient complications.