Abstract: Objective: To observe the of total prostate specific antigen in serum of patients with acute prostatitis (T-PSA), free prostate specific antigen (F-PSA), free prostate specific antigen / total prostate specific antigen (F/T) ratio, to explore the pathophysiological mechanism of acute prostatitis caused by increased PSA. Methods: in 34 cases of acute prostatitis patients respectively before treatment and 1 weeks after treatment, 3 months for detection of T-PSA, F-PSA value, F/T ratio was calculated. Results: Patients after 1 weeks and 3 months after treatment the serum T-PSA and F-PSA were lower than those before therapy (P0.05~P0.01), 3 months after treatment the serum T-PSA is less than 1 weeks after the treatment (P0.05); after 3 months of treatment F/T was higher than that before treatment (P0.05), before and after treatment the difference 1 weeks of F/T was 3 months and after treatment were not statistically significant (P0.05). After 3 months of treatment, 7 patients with PSA is greater than 4 ng/ml, treated by transurethral resection of the prostate or prostate biopsy, including 1 cases of prostate cancer, the rest are benign prostatic hyperplasia and inflammatory cell infiltration.Conclusions: acute prostatitis can lead to serum T-PSA, F-PSA were significantly increased, F/T decreased; the mechanism is prostatitis formation in normal prostate epithelial blood barrier damage and inflammatory hyperemia prostate gland proliferation of epithelial cells secrete more PSA. Dynamic observation of PSA for prostatitis and prostate cancer diagnosis and differential significance.