Abstract: Objective To investigate the effect of testosterone on the expression of androgen receptor (AR) in human monocytic cell line THP-1. Methods Cultured THP-1 cells were stimulated by testosterone with different concentrations and the AR protein was examined by Western blotting. Results AR expression was observed in unstimulated THP-1 cells and the quantity of AR expression was reduced by testosterone treatment in a dose-dependent manner. A selective AR blocker com- pletely abolished this inhibitory effect of testosterone on AR expresison. Conclusion Testosterone simulation time- and dose- dependently reduces AR expression in THP-1 cells.