Background: Atezolizumab plus bevacizumab (AteBev) has been established as a standard of care for patients with untreated advanced hepatocellular carcinoma (HCC). Lenvatinib was once the first choice and remains a treatment option for such patients; however, no subsequent treatment to date has proven a similar level of efficacy. This study aimed to evaluate the efficacy of AteBev in patients with HCC previously treated with lenvatinib. Methods: In this single-center, open-labeled, single-arm, phase II study, patients with advanced HCC previously treated with at least one systemic treatment were enrolled to receive 1,200 mg of atezolizumab and 15 mg/kg of bevacizumab intravenously every 3 weeks. The primary endpoint was progression-free survival (PFS). Secondary endpoints included overall survival, response rate, tumor control rate, and frequency of adverse events. The threshold and expected PFS were 3 months and 6.8 months, respectively, at a one-sided significance level of 0.05, and statistical power of 80%. Based on these data, the number of patients required was estimated to be 26. Results: Among 29 patients enrolled between November 2020 and October 2022, 26 previously treated with lenvatinib were included in the primary efficacy analysis. Median PFS was 9.70 [90% confidence interval (CI), 5.10–14.24] months. Median overall survival was 17.23 (90% CI, 3.18–27.85) months, and response rate and tumor control rate were 34.6% and 69.2%, respectively. Severe adverse events were observed in six patients (23.1%), six patients (23.1%) discontinued treatment because of immune-related adverse events or treatment-refractory ascites, and 10 patients (38.5%) required the withdrawal of treatment mainly because of proteinuria. There were no treatment-related deaths. Conclusions: AteBev for patients with advanced HCC previously treated with lenvatinib had a comparable efficacy to that in patients with no prior treatment. It may therefore be a treatment option for patients with advanced HCC previously treated with lenvatinib. Clinical trial information: jRCT1041200068.