<b><i>Introduction:</i></b> The study aimed to investigate the diagnostic utility of diffusion-weighted MRI (DW-MRI) in differentiating residual bladder cancer from benign postoperative changes before a second transurethral resection of the bladder (TURB). <b><i>Materials and Methods:</i></b> Of the 75 bladder cancer patients who underwent a second TURB from 2013 to 2015, 23 patients who underwent multi-sequence bladder MRI after their initial TURB were retrospectively evaluated. Thirty lesions were histologically examined at the second TURB and the results of them were compared with the findings obtained through T2-weighted MRI, dynamic contrast-enhanced MRI (DCE-MRI), and DW-MRI. <b><i>Results:</i></b> Positive findings of 27, 28, and 15 lesions showed up on T2W-, DCE-, and DW-MRI, respectively. Thirteen lesions were confirmed histologically to constitute residual cancer. The sensitivity/specificity/accuracy of T2W-, DCE-, and DW-MRI were 100/18/53, 100/12/50, and 92/82/87%, respectively. DW-MRI was significantly superior in specificity and accuracy to T2W- (<i>p</i> < 0.01 for both) and DCE-MRI (<i>p</i> < 0.01 for both). <b><i>Conclusions:</i></b> This study first showed the superiority of DW-MRI to T2W- and DCE-MRI in differentiating residual cancer before a second TURB.