Background: Cancer of the urinary bladder is the second most common malignancy of the genitourinary system. For the radiological evaluation of the urinary bladder and prostate gland, magnetic resonance imaging (MRI) is a valuable imaging modality due to high tissue contrast, multiplanar imaging capabilities, and the possibility of tissue characterization. Objective: The aim this study was to prospectively evaluate the ability of diffusion weighted magnetic resonance imaging (DW-MRI) in determining the T stage of bladder cancer and to correlate between the apparent diffusion coefficient (ADC) and histologic grade. Patients and method: This study included 30 patients with bladder mass. Results: The over all accuracy (stage by stage) is better in DWI than T2WI and post contrast image, 83.3%, 56.7% and 42.9% respectively. The mean ADC value is high in low grade tumors and low in high grade tumors with a cut off value of 0.83 mm2/s x10-3. Conclusion: We assume that DW-MRI is a safe and confident method in detection and local staging of urinary bladder carcinoma. In addition, ADC value can predict the histological grade of the tumor. Hence, DWI may be added to routine imaging protocols of urinary bladder tumors.