Background: Immune checkpoint inhibitors (ICI) targeting PD-1/L1 or in combination with CTLA-4 have shown therapeutic benefit in patients with advanced hepatocellular carcinoma (aHCC). This study aimed to evaluate the safety, tolerability, and preliminary efficacy of IBI310, an anti-CTLA-4 monoclonal antibody (mAb), combined with sintilimab, in patients with aHCC who failed or intolerant to previous systemic therapy. Methods: Three cohorts were pre-designed to explore recommended dose of IBI310 in de-escalation order: sintilimab 200 mg plus IBI310 3, 2 or 1 mg/kg every 3 week (q3w). Patients will receive the combined treatment up to 4 cycles, followed by sintilimab 200 mg q3w up to 24 months. Primary endpoint was safety. Key secondary endpoints included objective response rate (ORR), disease control rate (DCR), progress free survival (PFS) and overall survival (OS) by RECISTv1.1 per investigators. Results: 9 subjects were initially treated with sintilimab 200 mg plus IBI310 3 mg/kg q3w without predefined adverse event (AE) observed. 3 mg/kg was determined as recommended dose of IBI310 and no subject was assigned to other cohorts. As of the data cut-off of August 30, 29 subjects were enrolled (median age 51.4 years, 86.2% male, 96.6% BCLC C, 24.1% ICI treated). The average treatment cycles of IBI310 and sintilimab were 2.8 and 5.7. The most frequent treatment related adverse events (TRAEs) of any grade were alanine transaminase increases (34.5%), aspartate transaminase increases (34.5%), thrombopenia (24.1%), and lipase increases (24.1%). Grade ≥3 TRAEs occurred in 34.5% of subjects (including one grade 5 immune-mediated pneumonitis). Dose interruption and discontinuation rates due to AE were 55.2% and 6.9%. With a median follow-up of 9.89 months, investigator confirmed ORR and DCR were 17.2% (all partial response, including one anti-PD1 mAb failed) and 72.4%. The median PFS was 3.9 months (95% CI: 2.6, NR) and median OS not reached (95% CI: 11.4, NR). The 6-month PFS and OS rates were 45.8% (95%CI 25.2%, 64.2%) and 93.1% (95%CI 75.1%, 98.2%) respectively. 6 patients remain on treatment at cutoff date. Conclusions: The combination of sintilimab and IBI310 shows promising efficacy and managable safety profile in aHCC patients. Our results are comparable to that have been published in the same setting. This regimen is currently being evaluated in phase II study. Clinical trial information: NCT04401813.