Purpose: In resource-limited settings, family caregivers (FCGs) of adult cancer patients (ACPs) function in a context marred by high patient symptom burden, limited cancer care services and support and high caregiving burden. Despite this predicament, little is known about the quality of life (QoL) of FCGs in these settings. The study aimed to explore the determinants of QoL among FCGs of ACPs in Uganda.; Methods: A cross-sectional design was used to collect data from 284 FCGs of ACPs. The study questionnaire was composed of the Katz Index, Family Pain Questionnaire, modified Chronic Pain Self-efficacy Scale and the Caregiver Quality of Life-Index-Cancer.; Results: The mean age of FCGs was 36 ± 13.8 years. Most ACPs had stage 3 or 4 cancer (56%), severe pain (66.2%), reported moderate pain relief (51.1%) and were on chemotherapy (60.9%). The overall QoL of FCGs (70.2 ± 20.3) was moderate and 46.8% had low QoL. Most FCGs had high positive adaptation or financial concerns (55.3%) and low QoL in terms of burden (50.7%), disruptiveness (53.5%) and support (56.7%). The main determinants of overall QoL were FCGs' knowledge and self-eficacy for cancer pain management. The determinants of burden, disruptiveness, support and positive adaptations and financial concerns are reported.; Conclusion: The key determinants of the QoL of FCGs were knowledge and self-efficacy for cancer pain management. In Uganda and similar settings, interventions to build FCGs capacity in cancer-related pain and other symptom management may help to enhance the QoL of FCGs and the ACPs.