Diffusion-weighted (DW) magnetic resonance imaging (MRI) is a functional imaging to assess molecular diffusion. We report a first case of female urethral diverticular abscess examined by DW MRI. A 49-year-old woman presented with perineal pain, pyuria and inflammatory reaction. Conventional MRI revealed urethral diverticulum with the content of slightly lower-signal-intensity than urine on T2-weighted contrast. On DW MRI, the diverticulum was shown as a marked hyperintense lesion with restrained signal background of the surrounding tissue. The low apparent diffusion coefficient value of the diverticulum indicated high viscosity restricting water diffusion. DW MRI could depict urethral diverticular abscess clearly and easily in a non-invasive manner.