Objective To investigate the impact of preoperative body mass index (BMI) on the survival and prognosis of patients with hepatocellular carcinoma (HCC) complicated with type 2 diabetes mellitus after radical resection. Methods The clinical data of 140 HCC patients with type 2 diabetes mellitus who underwent radical resection in The Third Affiliated Hospital of Naval Medical University (Second Military Medical University) from Jan. 2013 to Dec. 2014 were retrospectively analyzed. These patients were divided into 2 groups based on preoperative BMI (ranged 18.8-31.8 kg/m²): normal-BMI (18.8-24.9 kg/m²) group and high-BMI (25.0-31.8 kg/m²) group. The basic clinical data and prognostic factors of the 2 groups of patients were summarized and analyzed. Results Among the 140 patients, 94 (67.1%) and 46 (32.9%) were in the normal-BMI and high-BMI groups, respectively. There was no significant difference between the 2 groups in age, gender, laboratory examination indicators, pathological parameters, antiviral treatment, diabetes treatment, or postoperative preventive transcatheter arterial chemoembolization (all P＞0.05). The 3-year overall survival rate of the high-BMI group (86.0%) was higher than that of the normal-BMI group (64.8%), and there was a significant difference in the overall survival between the 2 groups (P＝0.011). Multivariate Cox proportional hazard regression analysis showed that high-BMI was an independent protective factor for the overall survival of HCC patients with type 2 diabetes after radical resection (hazard ratio＝0.379, 95% confidence interval 0.156-0.917, P＝0.031). Conclusion HCC patients complicated with type 2 diabetes mellitus with high preoperative BMI have significantly better overall survival.