Purpose: To evaluate the impact of postoperative radiotherapy (PORT) on patterns of failure and survivals in uterine carcinosarcoma patients treated with radical surgery. Materials and Methods: Between October 1998 and August 2010, 19 patients with stage I-III uterine carcinosarcoma received curative hysterectomy and bilateral salpingo-oophorectomy with or without PORT at Seoul National University Hospital. Their hospital medical records were retrospectively reviewed. PORT and non-PORT groups included 11 and 8 patients, respectively. They were followed for a mean of 22.7 months (range, 7.8 to 126.6 months). Results: At 5 years, the overall survival rates were 51.9% for entire, 61.4% for PORT, and 41.7% for non-PORT groups, respectively. There was no statistical difference between PORT and non-PORT groups with regard to overall survival (p = 0.682). Seven out of 19 (36.8%) patients showed treatment failures, which all happened within 12 months. Although the predominant failures were distant metastasis in PORT group and loco-regional recurrence in non-PORT group, there was no statistically significant difference in locoregional recurrence-free survival (LRRFS) (p = 0.362) or distant metastasis-free survival (DMFS) (p = 0.548). Lymph node metastasis was found to be a significant prognostic factor in predicting poor LRRFS (p = 0.013) and DMFS (p = 0.021), while the International Federation Gynecology and Obstetrics (FIGO) stage (p = 0.043) was associated with LRRFS. Conclusion: Considering that adjuvant radiotherapy after surgical resection was effective to decrease loco-regional recurrence and most treatment failures were distant metastasis, multimodal therapy including surgery, radiotherapy, and chemotherapy might be an optimal treatment for uterine carcinosarcoma patients.