527 Background: Microvascular invasion (MVI) is a risk factor for recurrence after hepatectomy for hepatocellular carcinoma (HCC) patients. This study aimed to investigate to efficacy and safety of postoperative adjuvant transarterial infusion chemotherapy (TAI) with FOLFOX regimen for HCC patients with MVI. Methods: In this prospective, phase III, randomized, open-labeled, controlled clinical trial, HCC patients with histologically confirmed MVI were randomly assigned (1:1) after hepatectomy to receive either 1-2 cycles adjuvant TAI (AT group) or follow-up without any adjuvant treatment (FU group). The primary endpoint was disease-free survival (DFS), the secondary endpoints are overall survival (OS) and safety. Results: Between June, 2016 and April 2019, 127 patients were randomly assigned to AT group (n=63) or FU group (n=64). Clinicopathological characteristics were balanced between the two groups. The 6-, 12-, and 18-month OS rates for AT group were 100.0%, 97.7%, and 97.7%, and were 94.5%, 89.6%, and 78.5% for FU group, respectively. The 6-, 12-, and 18-month DFS rates for AT group were 84.7%, 61.8%, and 58.7%, and were 62.9%, 48.1%, and 38.6% for FU group, respectively. The OS and DFS were significantly better in AT group than in FU group (p=0.037 and 0.023, respectively). No patients in AT group experienced grade 3 or more severe adverse events (AEs). Conclusions: Adjuvant TAI after hepatectomy may bring survival benefits of OS and DFS for HCC patients with MVI. Clinical trial information: NCT03192618.