The association between skeletal muscle mass and postoperative morbidity in cancer patients has been demonstrated, but the results are not conclusive. The study aims to determine the predictive efficacy of rectus abdominis muscle (RAM) and psoas major muscle (PMM) thickness and other factors such as age, American Society of Anesthesiologists (ASA) score, operation duration, obesity, preoperative inflammatory markers, and pathological findings for postoperative morbidity. One hundred forty-one patients who underwent total abdominal hysterectomy + bilateral salpingo-oophorectomy + retroperitoneal lymphadenectomy + omentectomy for endometrial cancer were assessed retrospectively. Standard procedures (antibiotic prophylaxis and thromboembolism prophylaxis) were applied pre- and postoperatively, and the thicknesses of the RAM and PMM were measured by computed tomography. Postoperative morbidity was defined in the 3-month postoperative period as patients treated with a diagnosis of postoperative infection, those who developed pulmonary complications, thromboembolic complications, lymphatic drainage disorders, intracranial hemorrhage, and mortality. The mean thickness of the right-left RAM in the morbidity group was 7.4±2.1 mm, and 8.2±2.1 mm in the group without morbidity (p=0.038). On the other hand, the thickness of the right-left PMM was similar in both groups. When the predictive cut-off value for RAM thickness was 7.52 mm, the sensitivity, specificity, and negative and positive predictive values were 54.2%, 65.6%, 73.5%, and 44.8%, respectively. Advanced age, high ASA score, and extended operation duration were associated with an increased risk of morbidity in univariate analysis. However, multivariate analysis revealed that only age and operation duration were independent risk factors for postoperative morbidity [respectively, odds ratio (OR): 1.06, 95% confidence interval (CI): 1.01-1.12, p=0.033 and OR: 1.003, 95% CI: 1.0003-1.007, p=0.039]. Age and operation duration were identified as independent risk factors for predicting postoperative morbidity. However, it has been shown that a more comprehensive evaluation, including RAM thickness and ASA score alongside these two factors, could provide more definitive results.