Background and aims:Lenvatinib(LEN)is a newly developed tyrosine kinase inhibitor,and is approved as a first-line treatment for advanced hepatocellular carcinoma(HCC)in Japan.This retrospective multi-center study investigated the effect of the relative dose intensity(RDI)of LEN on response rate,progression-free survival(PFS),and overall survival(OS). Methods:This retrospective study enrolled 123 patients with advanced HCC who were treated with LEN at six hospitals in Japan between March 2018 and December 2019.These patients were divided into two groups:RDI ≥70％(RDI 70 group,N=70)or RDI＜70％(control group,N=53)in the first 30 days.The following data were compared between groups:patient backgrounds,adverse events,treatment out-comes,PFS,and OS.PFS and OS were analyzed using the Kaplan-Meier method,followed by the log-rank test.To identify significant factors that contributed to response,PFS,and OS,multivariate analysis was performed using factors for which P-values were ＜0.10 in univariate analysis. Results:The proportion of patients with Child-Pugh class 5A was significantly greater in the RDI 70 group than that in the control group(64.3％ vs. 28.3％,P＜0.01).Dose interruption due to adverse events was significantly more common in the control group.The response rate was significantly higher in the RDI 70 group than that in the control group(35.7％ vs. 11.3％,P＜0.01).Median PFS was significantly longer in the RDI 70 group(9.4 vs.4.7 months,P＜0.01).Multivariate analysis showed that RDI ≥70％(hazard ratio(HR)=0.55,P=0.025),hypertension grade ≥2(HR=0.47,P=0.019),and response(HR=0.52,P=0.033)were independently associated with improved PFS.Median OS was also significantly longer in the RDI 70 group(20.0 vs.13.3 months,P=0.045).Multivariate analysis showed that female sex(HR=0.33,P=0.034)and disease control(HR=0.31,P＜0.01)were independently associated with improved OS.RDI ≥70％ was not statistically significant in multivariate analysis. Conclusions:Our study revealed the importance of achieving RDI ≥70％ in the first 30 days of treatment to maximize the effects of LEN.