To compare the imaging quality, diagnostic accuracy and ADC values between reduced field-of-view diffusion-weighted imaging (rFOV DWI) and single-shot echo-planar-imaging DWI (fFOV DWI) in non-muscle-invasive and muscle-invasive bladder cancer. Bladder cancer is the most common malignant tumor of the urinary tract, and the incidence rate of bladder cancer is 6% for men and 2% for women[1]. Clinical treatment of bladder cancer depends on the level of muscle invasion (stage T2 or higher) or non-invasion of the muscle of the bladder wall (stage T1 or lower). Non-invasive tumors are mainly treated with transurethral resection (TUR) [2], whereas invasive tumors are mainly treated with radical cystectomy [3]. Therefore, it’s important to precisely differentiate between non-muscle-invasive and muscle-invasive bladder cancer before treatment.This study was approved by the local institutional review board. All patients gave written informed consent. 39 patients with a total of 60 bladder tumors underwent rFOV and fFOV DWI. The pathologic and histologic grades were determined for all tumors. Two observers rated the two DWI image quality and specified ascore using a 4-point scale (1, nondiagnostic; 4, excellent). Two radiologists who were blinded to the pathology findings reviewed three image sets (T2-weighted alone, T2-weighted plus fFOV DWI and T2-weighted plus rFOV DWI), and assigned T stages and confidence levels for tumors of stage T2 or higher. The image quality scores for the two DWI sequences were assessed by the Wilcoxon signed rank test. Differences in the diagnostic accuracy, sensitivity, and specificity for each image set were evaluated using the McNemar test. Differences in the performance were analyzed by comparing the areas under the receiver operating characteristic curves (Az values). The Mann-Whitney U test was used to compare the mean ADCs in the relationship between the tumor stage and histologic grade.The average image quality scores were 3.62 and 2.98 on rFOV and fFOV DWI, respectively, a significant difference (P=0.000). The diagnostic accuracies were 57%, 70%, 78% for T2-weighted images alone, T2-weighted plus fFOV DWI and T2-weighted plus rFOV DWI, respectively. The overall accuracy, specificity, and Az for diagnosing T2 or higher stages were significantly improved by adding rFOV DWI (P＜0.05). The mean ADC of muscle-invasive or G3 bladder cancers were significantly lower than for non-muscle-invasive or G1ones regardless of using fFOV or rFOV DWI (P<0.01). rFOV DWI is better compared to fFOV DWI regardless of imaging quality or diagnostic accuracy, and it is more conducive to identify whether bladder cancer invades the bladder muscle layer. And the ADC values can both be used to distinguish non-muscle-invasive or G3 from muscle-invasive or G1 bladder cancers.