Objective To evaluate the ability of ultra-high-b-value diffusion weighted imaging (DWI) in diagnosis of the prostate cancer (PCa) at 1.5T MR.Methods 12 patients with PCa and 17 patients with benign prostate hyperplasia (BPH) proved by histopathology underwent MRI and DWI examinations (b=400, 800,1 400 s/mm2).The signal intensity and visual degree of region of interest (ROI) in all DWI with different b values were respectively measured.The signal intensity and visual degree of ROI between high-b-value DWI and ultra-high-b-value DWI were compared,respectively.Results The difference of signal intensity of PCa between high-b-value DWI and ultra-high-b-value DWI was statistically significant (χ2=220.957,P=0.000<0.05).The signal intensity of PCa was getting brighter in DWI with higher b value.The difference of visual degree between these two groups was also statistically significant (χ2=11.378,P=0.003<0.05).The difference among PCa, BPH and normal prostate peripheral zone was statistically significant in ultra-high-b-value DWI (χ2=25.913, P=0.000<0.05).The brightness of PCa in ultra-high-b-value DWI mainly was bright or grey-bright (71.4%), while the brightness of BPH and normal prostate peripheral zone were mainly dark or grey-dark (BPH 63.0%, normal prostate peripheral zone 73.3%).The difference of visual degree among PCa, BPH and normal prostate peripheral zone was statistically significant difference as well (Z=-6.908,-6.110,P=0.000<0.017).The diagnostic efficiency of the signal intensity and visual degree were highest with b=1 400 s/mm2.Conclusion DWI with ultra-high-b-value can improve the display rate of the PCa at 1.5T MR, making easier the detection and diagnosis of PCa.