Background and Aim: This study aimed to investigate whether telephone follow-up by clinical pharmacists for unresectable hepatocellular carcinoma (HCC) patients treated with lenvatinib (LEN) contributes to improved adherence and treatment duration for LEN. Methods: This retrospective study enrolled 132 patients with HCC who were treated with LEN. The patients were classified into non-telephone follow-up (n = 32) or telephone follow-up groups (n = 100) [the latter group was further classified into family-pharmacist (FP) telephone follow-up (n = 18), or hospital family-pharmacist (HFP) telephone follow-up (n = 82) groups].Results: The progression-free survival (PFS) in the telephone follow-up group was significantly higher than that in the non-telephone follow-up group (PFS 6.1 months vs 3.7 months, P = 0.001, respectively). Although treatment duration was significantly longer in the telephone follow-up group than in the non-telephone follow-up group [median treatment duration: 10.4 months vs 4.1 months, P = 0.001, respectively.], no significant differences were noted between the HFP telephone follow-up group and FP telephone follow-up groups (10.3 months vs 13.3 months, P = 0.543). Self-interruption and adverse-event discontinuation in the HFP-telephone follow-up group were significantly lower than those in the FP-telephone and non-telephone groups (0% vs 11.1% vs 18.8%; P < 0.001, 25.6% vs 33.3% vs 53.1%; P = 0.022, respectively). Conclusions: Telephone follow-up contributes to prolonged treatment duration for LEN in patients with HCC treated. Moreover, telephone follow-up with an HFP may further improve treatment adherence.