Aim: Recently, more attention has been paid to the role of nutritional intervention in preventing the side effects of chemotherapy in oncology patients. Therefore, the aim of the present study was to analyze the effects of oral nutritional supplements on the body composition and biochemical parameters in women with breast cancer receiving postoperative adjuvant chemotherapy. Patients and Methods: The study involved women diagnosed with breast cancer who underwent surgical treatment and were qualified for chemotherapy (doxorubicin and cyclophosphamide). Women were divided into two groups, depending on whether oral nutritional supplements were used during chemotherapy. Anthropometric and biochemical parameters were analyzed twice in all patients: before and after six weeks of chemotherapy. Propensity score (PS) matching was performed to select patients balanced in terms of age, BMI, and clinicopathological features of the tumor. Statistical comparisons were conducted in a propensity-matched cohort of patients. Results: The value of BMI was maintained constant in the supplemented women older than 56 years after six weeks of chemotherapy. Regardless of age in the supplemented women, a significant increase in muscle mass, fat free mass (FFM), and fat free mass index (FFMI) was demonstrated. An increase in fat mass (FM) including visceral fat was observed only in the non-supplemented control. Regardless of age or initial FM, supplemented women exhibited a constant level of albumin. Moreover, in the supplemented women with normal initial FM, the stable values of triglycerides and HDL cholesterol were maintained after six weeks of chemotherapy. Conclusion: The present study demonstrated that oral nutritional supplements could improve body composition and prevent hypoalbuminemia and lipid abnormalities in women with breast cancer undergoing chemotherapy.