Family caregivers' quality of life (QOL) is an important indicator for end-of-life care, but appropriate assessment tools are unavailable in Taiwan. This correlational study therefore tested the psychometric properties of the Caregiver Quality of Life Index-Cancer Mandarin version (CQOLC-M) in 359 dyads of cancer patients with terminal illness and their family caregivers from 5 teaching hospitals throughout Taiwan. Caregivers' QOL, spiritual well-being, social support, pain intensity, and economic situation were assessed using the CQOLC-M and 4 established scales. The CQOLC-M had internal consistency reliability of .87. Construct validity was supported by factor analysis, hypothesis testing, and known-group comparison. Exploratory factor analysis showed 7 underlying factors explaining 48.15% of the variance. Caregiver Quality of Life Index-Cancer Mandarin version scores correlated moderately with caregivers' social support (P < .01) and spiritual well-being (P < .01). Caregivers' QOL was inversely related to both patients' (F = 4.90; P = .008) and caregivers' average pain (t = −4.22; P < .001) in the past 24 hours. We suggest removing 4 items with factor loading of less than 0.4. Since caregivers' QOL depends on patients' and caregivers' physical dimensions, we recommend adding physical-related items to the CQOLC-M. Clinicians can improve caregivers' QOL not only by maintaining their health, social support, and spirituality but also by better managing the pain of patients with terminal illness.