Background: To investigate the survival outcomes, the treatment toxicities, and the recurrence pattern of nineteen patients with retroperitoneal sarcoma treated with radiotherapy. Methods: The inclusion criteria for this retrospective study were previously untreated retroperitoneal sarcoma who had received radiotherapy. From March 2016 to June 2022, the chart records and images of 22 eligible patients were reviewed. There were ten males and twelve females, and their ages ranged from 34 to 80 years old (median 55). Sixteen patients (72.7%) had a liposarcoma, four patients (18.3%) had a leiomyosarcoma, one patient (4.5%) had a spindle cell sarcoma, and one patient (4.5%) had a malignant peripheral nerve sheath tumor with heterologous rhabdomyosarcomatous and liposarcomatous differentiation. At diagnosis, four patients (18.1%) had a stage I-II disease, eighteen patients (77.4%) had a stage III disease, and only one patient (4.5%) had a stage IV disease. Twenty one patients (95.5%) received operation, and nineteen of them had a positive or close ( < 1mm) surgical margin. Nineteen patients (86.4%) received adjuvant radiotherapy (median dose 5400cGy, ranging 5000 to 6300cGy), one patient (5.3%) received neoadjuvant radiotherapy (5000cGy), one patient received definitive chemoradiotherapy (7000cGy), and one patient received palliative radiotherapy (3000cGy) to bone metastasis. Results: The medial follow-up was 32 months, and the two-year overall survival rate was 79.8%. Acute toxicities of radiotherapy included gastrointestinal toxicities (grade 1-2: 9 patients), nausea (grade 1-2: 7 patients, grade 3-4: 3 patients), vomiting (grade 1-2: 3 patients, grade 3-4: 2 patients), neutropenia (grade 1-2: 2 patients, grade 3-4: 1 patients), and fatigue (grade 1-2: 5 patients). In patients without metastatic disease at diagnosis, two-year overall survival rate was 84.0%, and two-year disease-free survival rate was 62.9%. There were 8 recurrences (1 local alone, 2 distant metastasis alone, 1 local plus regional, 3 local plus distant metastasis, and 1 local plus regional plus distant metastasis), and 5 deaths. Recurrent metastatic locations included lung (n = 1), liver (n = 1), bone (n = 2), peritoneum (n = 1), distant lymph nodes (n = 1), and soft tissue of thigh (n = 1). One patient with metastatic disease at diagnosis expired due to disease progression with 8 months survival. Conclusions: Radiotherapy in retroperitoneal sarcoma provided an acceptable two-year survival rate with tolerable toxicities, but recurrence rate was still high. About 75.0% of recurrent events consisted of local recurrence, so close follow up of primary tumor area is necessary.