To report the efficacy and safety of postoperative adjuvant hepatic arterial infusion chemotherapy (HAIC) with 5-fluorouracil and oxaliplatin (FOLFOX) in hepatocellular carcinoma (HCC) patients with microvascular invasion (MVI).In this randomized, open-label, multicenter trial, histologically confirmed HCC patients with MVI were randomly assigned (1:1) to receive adjuvant FOLFOX-HAIC (treatment group) or routine follow-up (control group). The primary end point was disease-free survival (DFS) by intention-to-treat (ITT) analysis while secondary end points were overall survival, recurrence rate, and safety.Between June 2016 and August 2021, a total of 315 patients (ITT population) at five centers were randomly assigned to the treatment group (n = 157) or the control group (n = 158). In the ITT population, the median DFS was 20.3 months (95% CI, 10.4 to 30.3) in the treatment group versus 10.0 months (95% CI, 6.8 to 13.2) in the control group (hazard ratio, 0.59; 95% CI, 0.43 to 0.81; P = .001). The overall survival rates at 1 year, 2 years, and 3 years were 93.8% (95% CI, 89.8 to 98.1), 86.4% (95% CI, 80.0 to 93.2), and 80.4% (95% CI, 71.9 to 89.9) for the treatment group and 92.0% (95% CI, 87.6 to 96.7), 86.0% (95% CI, 79.9 to 92.6), and 74.9% (95% CI, 65.5 to 85.7) for the control group (hazard ratio, 0.64; 95% CI, 0.36 to 1.14; P = .130), respectively. The recurrence rates were 40.1% (63/157) in the treatment group and 55.7% (88/158) in the control group. Majority of the adverse events were grade 0-1 (83.8%), with no treatment-related death in both groups.Postoperative adjuvant HAIC with FOLFOX significantly improved the DFS benefits with acceptable toxicities in HCC patients with MVI.