Purpose: This study was to examine both the reliability and validity of the Japanese version of the Caregiver Quality of Life Index-Cancer (CQOLC), which was developed to measure the quality of life of family caregivers of cancer patients. Methods & Results: Study subjects comprised 400 family caregivers who were registered at an Internet research company. The explanatory factor analysis yielded the following 4 domains: psychological burden (8 items); positive emotions (5 items); and financial burden (3 items); disruption of daily living (5 items). The Cronbach's alpha coefficients of the total score and each domain were 0.85 and 0.75 to 0.88, respectively. The total score and each domain were moderately correlated with mental health, vitality, social functioning, general health, role emotinal scores from the SF-36. The intraclass correlation coefficients of the total score and each domain were 0.78 and 0.67 to 0.74, respectively. Conclusion: These results suggest that the Japanese version of the CQOLC has sufficient reliability and validity.