Objective To evaluate the diagnostic value of diffusion weighted MR imaging in retroperitoneal tumor using high field strength MR.Methods Eighty-one patients with suspected retroperitoneal tumor underwent DWI (b=0,600) or (b=0,800 s/mm2) using 1.5 or 3.0 T high strength MR.The apparent diffusion coefficient (ADC) values of all patients were measured by a radiologist unaware of the pathological results.The values of the low-value region in ADC map in retroperitoneal tumor were measured and recorded as the ADC values.The retroperitoneal tumors were divided into benign and malignant group according to the pathological results of surgery.The ADCs were compared between the benign group and the malignant group using t test.