Although hepatotoxicity has been rarely reported during adjuvant chemotherapy in breast cancer patients, we observed a high frequency in our patients who were also taking alternative agents. We therefore sought to determine the association between hepatotoxicity and alternative agents during adjuvant chemotherapy in breast cancer patients. All breast cancer patients were treated with the same chemotherapeutic regimen and had normal baseline liver function test (LFT). LFT was checked repeatedly during each cycle of chemotherapy. Patients showing LFT abnormalities were asked about use of alternative agents, and, after the end of chemotherapy, a questionnaire was administered to each patient on their use of alternative agents. Of 178 patients, 65 (36.5%) admitted using alternative therapy, and significantly more patients in this group developed LFT abnormalities (37/65, 56.9%) than those who denied taking alternative therapy (25/113, 22.1%, p=0.001). Although LFT abnormalities were mild to moderate and normalized in most patients after cessation of alternative agents, it remained a serious problem in one patient. In conclusion, alternative therapy may be one of the etiologies for abnormal LFT in breast cancer patients receiving adjuvant chemotherapy.