Context Cancer-related fatigue is one of the most commonly reported symptoms in cancer patients. Short but good assessment is essential to detect and manage this symptom. Brief Fatigue Inventory (BFI) is a valid and reliable short instrument to assess cancer-related fatigue. Objective To examine the validity and reliability of the Indonesian BFI. Methods Forward and backward translation approach, followed by cognitive debriefing process, was done to develop Indonesian BFI. One hundred twenty-one consecutive adult outpatients with cancer who are willing to participate in this study filled in Indonesian BFI along with the Medical Outcome Study Quality of Life Short Form 36 (MOS SF-36). Demographic and health data were collected. Results The Indonesian BFI had an overall Cronbach's alpha for the nine items of 0.956. The results of the factor analysis suggested a one-factor solution, supporting the hypothesis of unidimensionality of the Indonesian BFI. The Indonesian BFI score was compared with MOS SF-36 subscale to evaluate convergent validity. An expected inverse correlation between Indonesian BFI and all domains of MOS SF-36 was observed (r = −0.388 to −0.676; P < 0.0000). Discriminant validity analysis showed that the Indonesian BFI mean score significantly increased with increasing Eastern Cooperative Oncology Group Performance Status values (P = 0.000). Conclusion Indonesian BFI is a reliable and valid instrument for Indonesian cancer patients.