This study aimed to investigate the effect of being overweight on the outcome of ablation therapy for patients with early-stage hepatocellular carcinoma (HCC). This retrospective study included 198 patients with HCC who underwent radiofrequency ablation or microwave ablation at Gunma Saiseikai Maebashi Hospital between April 2017 and December 2021. We divided the patients into two groups based on their body mass index (BMI): overweight (BMI ≥ 25 kg/m2, n = 74 (37.4%)) and non-overweight (BMI < 25 kg/m2, n = 124 (62.6%)). The technical success rates (TSRs) in the first session were 78.4% and 90.3% in overweight and non-overweight patients, respectively, with a significant difference (p = 0.03). Additional ablation therapy for residual tumors was required in 15 (20.3%) overweight and 11 (8.9%) non-overweight patients (p = 0.03), resulting in 95.9% and 99.2% TSRs at the final session, respectively, without a significant difference (p = 0.3). While local tumor progression and distant recurrence rates were not significantly different between the two groups, overall survival was better in overweight patients than in non-overweight patients (p < 0.001). Despite the potential adverse impact of being overweight on public health problems, the present findings showed the relationship between being overweight and improved survival. The negative aspects of being overweight might remain as minor technical issues in HCC patients receiving ablation therapy.