Abstract Duvelisib, a small-molecule phosphatidylinositol 3-kinase-δ,γ inhibitor, has shown efficacy for mycosis fungoides (MF) at dosage ranges of 25-100 mg twice daily (BID), but with significant toxicity. We conducted a retrospective cohort study of patients with advanced MF treated with low-dose duvelisib (15 mg every other day to BID), in an effort to minimize toxicity. A total of 7 patients were included. The overall response rate on duvelisib was 71%, with the remaining patients maintaining stable disease. Mean modified Severity Weighted Assessment Tool score improved by 57.4% and mean percent body surface area involved improved by 52%. Median progression-free survival was 10.3 months. Adverse events occurred in 4 of 7 patients, the most common being fatigue (2/7; grades 1-2), nausea (2/7; grades 1-2), and transaminitis (2/7; grade 3). Overall, low-dose duvelisib showed efficacy for advanced MF with less toxicity, providing a rationale for its use as monotherapy and potentially combinatorial therapy.