Primary Ewing sarcoma/primitive neuroectodermal tumor (ES/PNET) of the kidney represents a spectrum of rare neoplasm with dismal clinical prognosis. This type of malignant tumor predominantly occurs in the soft tissue and bones of pediatric-young adults, and it may rarely arise from the kidney. Derived from the neuroectoderm, renal ES/PNET belongs to a group of primitive and aggressive tumors in its biological manifestation. Herein, we report the case of a 40-year-old pregnant woman with renal mass, in whom was found gross hematuria and slight lumbar acid during pregnancy. A computed tomography scan revealed an irregular soft tissue mass approximately 5×5×5 cm in size. The patient underwent robot-assisted laparoscopic nephrectomy of the right kidney after childbirth. The diagnosis of renal ES/PNET was confirmed by immunohistochemical detection and fluorescence in situ hybridization of the nephrectomy specimen. Primary renal ES/PNET represents a rare and lethal entity, especially in a 40-year-old pregnant woman. Although the clinical presentation of this tumor is nonspecific, renal ES/PNET frequently exert dismal prognosis and aggressive clinical outcomes. Thus, it is essential to distinguish ES/PNET from other renal cell carcinomas and carry out an optimum treatment strategy as soon as possible.