Objective: To evaluate the feasibility of MR diffusion-weighted imaging (DWI) in diagnosis of acute rejection after renal transplantation. Methods: Sixty-nine patients who underwent renal transplantation were enrolled in the study.According to the clinical features and renal biopsy,26 patients were designated in rejection group and 43 in non-rejection group.Patients in non-rejection group underwent MR DWI scan at 2 to 3 weeks after operation,and those in rejection group underwent scan at 5 d before or after renal biopsy.Then the apparent diffusion coefficient (ADC) values of transplanted kidneys were measured with high diffusion sensitivity gradient factors (b values). Results: Patients with acute rejection had significantly lower ADC (P≤0.05) than non-rejection patients with all the different b values (b=200,400,600,800,1 000 s/mm~2).The ROC curves showed that sensitivity and specificity were best when b value was 800 s/mm~2. Conclusion: DWI is a potential and reliable non-invasive method for the diagnosis of the acute rejection after renal transplantation.