Objective:To discuss the clinical features, treatment and prognosis of renal mesenchymal malignancy.Methods:Retrospective analysis was performed on the clinical data of 48 patients with renal mesenchymal malignancies admitted from January 2005 to June 2019.The patients' age ranged from 16-79 years, including 29 males and 19 females. There were 21 cases of Han nationality and 27 cases of ethnic minorities. The main complained of lumbago were 31 cases, bloating 8 cases, blood urine 2 cases, and 6 cases by physical examination. And one case was seen in orthopedics due to upper arm pain. The patient's completion of the examination indicated a tumor of kidney origin. CT examination mostly showed renal space-occupying lesions. After enhancement, the tumor was irregularly enhanced, with unclear edges, which was difficult to distinguish from renal carcinoma. The tumors were on the left in 30 cases and on the right in 18 cases. All patients perfected preoperative blood routine, biochemical, coagulation and other examinations. Prothrombin time was normal in 39 cases. Clinical staging was conducted according to the imaging results at the time of initial diagnosis. 7 were in clinical Stage T 1, 16 were in Stage T 2, 20 were in stage T 3, and 5 were in stage T 4.Distant metastases were found in 8 cases, including 4 lung metastases, 2 retroperitoneal metastases, and 2 bone metastases. 13 patients underwent needle biopsy to confirm the diagnosis. Among the 48 cases in this group, 29 cases were diagnosed as renal tumor, 12 cases were diagnosed as renal space occupying lesions, and 7 cases were diagnosed as retroperitoneal space occupying. 17 underwent radical nephrectomy, 22 underwent partial nephrectomy, and 9 did not receive surgical treatment after needle biopsy. Results:Among the 48 patients, Conventional pathology confirmed 17 cases as leiomyosarcoma, 17 cases as liposarcoma, and 14 cases as other types of mesenchymal malignancies. Follow-up ranged from 7 to 180 months, with an average follow-up of 38.8 months. Thirty patients died, and the average survival time was 39 months. The 5-year survival rates of leiomyosarcoma, liposarcoma and other types of tumors were 18.2%, 30.8% and 50.1%, and the difference was statistically significant ( P=0.047). The 5-year survival rates of patients with normal and abnormal prothrombin time were 36.8% and 11.0%, the difference was statistically significant ( P=0.018). The 5-year survival rates of radical surgery and partial nephrectomy were 44.6% and 29.8%, and the difference was statistically significant ( P<0.05). The 5-year survival rates of T 1, T 2, T 3 and T 4 patients were 40.0%, 31.6%, 35.4% and 0, and the differences were statistically significant ( P=0.020). Multivariate analysis showed that preoperative prothrombin time ( P=0.013), clinical T stage ( P=0.030) and surgical method ( P=0.006) were independent factors affecting the prognosis of patients with RMM. Conclusions:Renal mesenchymal malignant tumor is rare, and highly malignant. Preoperative needle biopsy did not affect the prognosis of RMM. Patients with normal prothrombin time, early clinical staging and radical surgery had better prognosis. Renal liposarcoma has a better prognosis than renal leiomyosarcoma.