We validated the Taiwanese version of the Brief Fatigue Inventory (BFI-T) in a sample of 439 Taiwanese patients with multiple cancer diagnoses. Internal consistency was indicated by Cronbach alphas of 0.96 for fatigue-related severity and 0.95 for interference. Test-retest reliability was 0.89 for fatigue severity and 0.91 for interference. Factor analysis revealed a one-factor structure. Convergent validity was examined by correlating the BFI-T worst fatigue and fatigue severity composite scores with POMS vigor and fatigue subscales scores. Known-group validity was established by comparing BFI-T worst fatigue and severity composite scores between patients with low functional status and high functional status and between inpatients and outpatients. The BFI-T's sensitivity was examined by comparing BFI-T severity and interference composite scores before, during, and after chemotherapy treatment in a subsample of 20 breast cancer patients. The BFI-T is reliable, valid, and sensitive for measuring cancer-related fatigue severity and interference among Taiwanese cancer patients.