Abstract To validate the efficacy and safety of thymosin α-1 combined with lenvatinib plus sintilimab in the treatment of unresectable hepatocellular carcinoma. Patients with unresectable hepatocellular carcinoma treated with lenvatinib plus sintilimab at the People’s Hospital of Guangxi Zhuang Autonomous Region from January 2020 to June 2022 were retrospectively analyzed. The patients were divided into an experimental group and a control group based on their therapeutic regimens: thymosin α-1 plus lenvatinib and sintilimab (experimental group), and lenvatinib plus sintilimab (control group). The primary endpoints were overall survival and progression-free survival. Tumor response was evaluated according to mRECIST criteria, and the partial response, complete response, stable disease, progressive disease, object response rate, and disease control rate of the two groups were compared. Adverse events were evaluated using the Common Terminology Criteria for Adverse Events version 5.0. The median overall survival of all patients was 13.0 months (95% CI 10.587–15.413). The experimental group had a longer median overall survival than the control group (16 months vs. 11 months, P = 0.018). The median progression free survival of all patients was 5.0 months (95% CI 3.721–6.279). The experimental group had a longer median progression-free survival than the control group (7 months vs. 4 months, P = 0.006). The objective response rate of the experimental group was 55.8% (24/43), and of the control group’s 34.7% (17/49) (P = 0.042). The disease control rate of the experimental group was 76.7% (33/43), while the control group had a rate of 59.2% (29/49) (P = 0.073). There was no significant difference in the incidence of grade 1–2 adverse events or grade 3–4 adverse events between the two groups (P > 0.05). Thymosin α-1 combined with lenvatinib plus sintilimab is an effective and safe therapeutic regimen in unresectable hepatocellular carcinoma.