Abstract Background Sarcopenia is defined as the loss of skeletal muscle mass, accompanied by decreased muscle strength, and consists of myopenia and myosteatosis. Recent evidence has suggested the predictive value of sarcopenia for the risk of perioperative and oncological outcomes in various malignancies. The aim of this study was to clarify the clinical impact of myopenia and myosteatosis in colorectal cancer (CRC) patients. Methods We analyzed the preoperative psoas muscle mass index and intramuscular adipose tissue content using preoperative computed tomography images from 308 CRC patients using statistical methods. Results Despite no significant correlation between myosteatosis and prognosis, preoperative myopenia significantly correlated with clinicopathological factors for disease development, including advanced tumor depth ( P = 0.009), presence of lymphatic vessel invasion ( P = 0.006), distant metastasis ( P = 0.0007), and advanced stage classification ( P = 0.013). Presence of preoperative myopenia was an independent prognostic factor for both cancer‐specific survival (hazard ratio [HR]: 2.75, 95% confidence interval [CI]: 1.5–5.05, P = 0.001) and disease‐free survival (HR: 3.15, 95% CI: 1.8–5.51, P = 0.0001), and was an independent risk factor for postoperative infectious complications in CRC patients (odds ratio: 2.03, 95% CI:1.17–3.55, P = 0.013). Furthermore, these findings were successfully validated using propensity score matching analysis. Conclusions Preoperative myopenia could be useful for perioperative management, and quantification of preoperative skeletal muscle mass could identify patients as a high risk for perioperative and oncological outcomes in CRC patients.