Abstract: Objective To investigate the expressions of prostatic specific antigen (PSA) mRNA in mononuclear cells of the peripheral blood in prostate cancer patients and controls and discuss its clinical significance. Methods 39 patients with prostate cancer and 12 healthy men were selected (normal control group). 5 mL anticoagulant blood was collected in every individual. The expressions of PSA mRNA in the mononuclear cells of the peripheral blood were measured by RT-PCR after delamination of the mon oclear cells. Results ①26 of 39 (66.7%) patients had positive PSA mRNA expression, in which (23 cases) serum PSA＞20.0 μg·L^-1, positive rate of PSA mRNA expression was 87.9% (20/23), while those serum PSA≤20.0 μg·L^-1, positive rate of PSA mRNA expression was 37.5% (6/16). ②In the 6 cases whose PSA mRNA was positive and serum PSA ≤20.0 μg·L^-1, the distribu tion of the biopsy Gleason were 1-4 score 0/3，5-7 score 1/8，8-10 score 5/5, pathologic findings revealed middle and low differentiation carcinoma in 6 patien ts with positive expression of PSA mRNA. Conclusion The detection of PSA mRNA has high sensitivity in prostate cancer patients whose serum PSA ＞20.0 μg·L^-1, which is a reliable method. The detection of PSA mRNA in mononuclear cells of peripheral blood can predict the micrometastasis in prostate cancer patients whose PSA≤20.0 μg·L^-1.