To investigate the effects of down-regulation of prostate androgen regulated (PAR) expression on proliferation of PC3 cells by using RNA interference (RNAi), suppression of PAR expression was achieved by transfection of PC3 cells with short hairpin RNA (shRNA) expression vectors against PAR, designated as psiRNA-PAR1, psiRNA-PAR2 and psiRNA-PAR3. The inhibitory effects were confirmed by RT-PCR. The growth features of PC3 transfectants were analyzed by cell counts, colon formation in soft agar and flow cytometry. The expression of PAR was suppressed by the three shRNA expression vectors. psiRNA-PAR1 was shown to inhibit the PAR expression most efficiently, with the inhibitory rate reaching a peak at (81.18+/-1.68)% 48 h after the transfection. PC3 transfectants exhibited a decreased proliferation in cell culture and a low efficiency of colon formation in soft agar. Flow cytometry revealed a G(2)/M arrest and induced apoptosis. Down-regulated PAR expression inhibited the growth of PC3 cells by inducing G(2)/M arrest and activating apoptotic pathway. As a potential proto-oncogene that triggers and/or has persistent malignant proliferation, PAR may serves as a very target for the gene therapy.