Objectives <p>To evaluate the prognostic impact of CT-derived body composition metrics and clinical factors, and to develop a prognostic model in patients with stage II rectal cancer.</p> Materials and methods <p>This retrospective study analyzed consecutive stage II rectal cancer patients who underwent radical surgery. The predictive value of body composition metrics and clinical factors was evaluated. A Cox proportional hazards model-derived nomogram, based on independent risk factors identified through univariate and multivariate analyses, was established and validated to predict overall survival (OS).</p> Results <p>Among 975 patients (median age 63 years, IQR 55–70 years; 644 [66.1%] males), 183 deaths were recorded during a median follow-up period of 53 months (IQR 33–83 months). Low skeletal muscle density (SMD) (OR = 0.43; 95% CI: 0.20, 0.91), age ≥ 65 years, and CA125 positive (<i>p</i> &lt; 0.05) were risk factors for severe postoperative complications. High visceral-to-subcutaneous adipose ratio (VSR) (OR = 1.33; 95% CI: 1.02, 1.73), body mass index (BMI) &gt; 24.9, and T4 stage (<i>p</i> &lt; 0.05) were risk factors for prolonged hospitalization. After univariate and multivariate analyses, the nomogram based on age, gross type, perineural invasion, lymphovascular invasion, inflammatory burden index, subcutaneous fat area (SFA), and SMD (<i>p</i> &lt; 0.05) exhibited area under the curve values of 0.77/0.62, 0.77/0.62, and 0.75/0.67 at 1-year, 3-year, and 5-year OS in training/validation sets, respectively.</p> Conclusions <p>In predicting the prognosis of stage II rectal cancer patients, VSR, SFA, and SMD were superior to other body composition metrics. The nomogram integrating body composition metrics and clinical factors showed superior predictive performance for OS compared to a single risk factor alone.</p> Critical relevance statement <p>CT-derived body composition metrics can predict the prognosis of rectal cancer patients by reflecting the nutritional and metabolic status.</p> Key Points <p><UnorderedList Mark="Bullet"> <ItemContent> <p>Body composition metrics’ prognostic utility in stage II rectal cancer is clear.</p> </ItemContent> <ItemContent> <p>Body composition metrics are associated with clinical outcomes in stage II rectal cancer.</p> </ItemContent> <ItemContent> <p>Body composition is a predictive biomarker for stage II rectal cancer.</p> </ItemContent> </UnorderedList></p> Graphical Abstract <p></p>