BACKGROUND: Cancer-related sleep disturbance is common and can adversely affect physical and mental health. Bright light (BL) therapy is a novel intervention that targets sleep by promoting circadian regulation. Emerging evidence suggests BL can improve sleep disturbance, symptom burden, and health-related quality of life in cancer and other populations; however, this research is limited. The present two-phase pilot study assessed the feasibility and preliminary intended effects of BL therapy on sleep in ovarian and endometrial cancer survivors, and explored biologic and chronobiologic factors that may underlie intervention effects. METHODS: In phase I, focus groups were conducted with 12 survivors and 9 gynecologic oncology clinicians to evaluate and gather feedback about the proposed study. In phase II, a pilot randomized controlled trial was conducted with 18 ovarian or endometrial cancer survivors who were randomized 1:1 to receive 45 min of BL or dim light (DL) for 4 weeks. Participants wore wrist actigraphs; completed sleep diaries and self-report questionnaires; and provided blood, saliva, and urine samples at baseline (T1), post-intervention (T2), and 3-month follow-up (T3). RESULTS: Study procedures were modified according to focus group results. Enrollment, retention, and adherence were all ≥ 80%. Mixed-model ANOVAs demonstrated that the number of nighttime awakenings per actigraphy, and sleep quality and depression per self-report, trended toward improvements in the BL condition compared to the DL condition. These variables improved from T1 to T2 before returning to baseline at T3. Effect sizes were generally medium to large. CONCLUSIONS: Study findings suggest that BL therapy is feasible among ovarian and endometrial cancer survivors. It may be an effective, non-pharmacological approach to reduce sleep disturbance and symptom burden in this population.