Objective To investigate the feasibility of differentiation between prostate cancer and prostatitis by using metabolic ratios provided by 3D 1H Magnetic Resonance Spectroscopic Imaging (MRSI). Methods Metabolic changes were evaluated in 42 voxels with prostate cancer and 30 voxels with prostatitis in the peripheral zone using MRSI. The results were based on the pathologic findings by biopsy. The (choline + creatine)/Citrate (CC/C) ratio and the changes of choline and citrate levels were evaluated in each voxel with cancer or prostatitis, t test was used to determine the power of the CC/C ratio in differentiation between prostate cancer and prostatitis. Results The CC/C ratio for cancer voxels (1.28±0.41) was significantly different from the ratio in the voxles with prostatitis (1.03±0.40), t=6.45, P<0.05, due to greatly increased choline level in the cancer voxels. When CC/C ratio of 0.8 was taken as the criteria for the diagnois of prostate cancer, the sensitivity, specificity and accuracy were 65.5%, 71.4% and 66.7%, respectively. Positive predictive value(PPV)and negative predictive value(NPV) were 90.5% and 33.3%, respectively. The CC/C ratio was higher than 0.86 in 66.7% voxels with prostatitis (20 voxels of total 30 voxels), which mostly depended on the level of choline. When citrate level was used as an auxiliary index to evaluate prostatitis (Cit/norm, Cit≥0.75), the misdiagnosis rate of prostate cancer was reduced to 26.6%(8 voxels of total 30 voxels). Conclusions The metabolic ratio of CC/C can be used to differentiate prostate cancer from prostatitis. The misdiagnosis rate is reduced when citrate is not or slightly decreased relative to normal citrate level (Cit/norm, Cit≥0.75).