Bachground: Ultrasound-guided large core needle biopsy technique has widely been applied in the diagnosis of adult abdominopelvic, mediastinal cavity, breast and neck tumors. There are few reports on ultrasound-guided biopsy using large-core needle in pediatric solid tumor. This study was to evaluate the ultrasound features and the diagnostic value of ultrasound-guided core needle biopsy for pediatric retroperitoneal tumors. Methods: The pediatric patients with retroperitoneal tumor that determined by ultrasound, CT or MRI examination and underwent ultrasound guided core needle biopsy from October 2018 to January 2020 were reviewed at Vietnam National Children’s Hospital. A minimum of five cores in each case was obtained. 13 patients were operated and had surgical pathology results. The ultrasound features and the diagnostic accuracy of ultrasound-guided core needle biopsy were evaluated. Results: Fifty - two patients (25 males, 27 females) were enrolled into the study. Conventional ultrasound examination showed irregular hypoechoic or mixed echo masses and calcification and liquefied necrosis. The ratio of vascular encased tumors was 61.5%. The quality of tissue sample was enough to make diagnosis was 98.1% (51/52). Only one case was misdiagnosed because of inadequate tissue sample. The diagnostic accuracy of ultrasound guided core needle biopsy compared to subsequent surgical histopathology was 76.9 % (10/13). Retroperitoneal tumor pathology varied with neuroblastic tumor was 86.3% (60.8% NB, 11.8% GNB and 13.7% GN), ACC was 5.9%, germ cell tumor was 4.0% (2.0% teratoma, 2.0% yolk sac tumor) and extra renal malignant rhadoid tumor was 2.0%. No serious complication, hemorrhage or infection occurred. Conclusions: Ultrasound-guided core needle biopsy seems to be an accurate, minimally invasive, and safe diagnostic method of pediatric retroperitoneal tumor.