Objective To retrospectively investigate combine diffusion-weighted imaging (DWI) and T2-weighted imaging for the prediction of extracapsular extension (ECE) in patients with prostate cancer, as well as to compare apparent diffusion coefficients (ADCs) between patients with and without ECE. Methods Seventy-six patients underwent 3T magnetic resonance imaging (MRI) before prostatectomy. Two experienced radiologists analyzed T2-weighted images alone and in combination with DWI in consensus and rated the likelihood of ECE. Tumor ADC values were measured, and the results were compared between patients with and without ECE. Results Of the 456 sectors studied, 74 (16%) were positive for ECE in 31 patients. the specificity and accuracy of combined T2-weighted imaging and DWI were 94.5% and 91.7%, respectively, superior to T2- weighted imaging alone (87.2% and 81.2%, respectively) (p<0.001). On receiver operating characteristic analysis, the area under the curve (Az) of combined T2-weighted imaging and DWI (Az=0.900) was significantly greater than that of T2-weighted imaging alone (Az=0.828) (p<0.001). The mean tumor ADC values were significantly lower in patients with ECE than patients without ECE (p<0.001). Conclusion DWI in addition to T2- weighted imaging improves the ability to predict ECE in patients with prostate cancer. Furthermore, tumor ADC values in patients with and without ECE are significance.