Studies have shown that miR-221 and miR-222 are deregulated in many cancers, including prostate cancer. Nevertheless, the biological role and the underlying mechanisms of miR-221 and miR-222 in the pathogenesis of androgen-independent prostate cancer are still not clear. The proliferation, apoptosis, cell cycle distinction, and migration capacity of prostate cells were determined following transfection of miR-221 or miR-222 inhibitor. The biological impact and regulation of SIRT1 on prostate cancer cells were investigated. MiR-221 and miR-222 were highly expressed in PC-3 cells compared with in LNCap cells. After miR-221 or miR-222 expression was inhibited, the proliferation and migration rates of PC-3 cells decreased and the apoptosis rate increased. Moreover, SIRT1 protein was up-regulated in cells after they were transfected with miR-221 or miR-222 inhibitor. Cells transfected with siSIRT1 showed increased migration and a decreased apoptosis rate, but there was no significant effect on cell proliferation compared with the controls. There was a negative correlation between miR-221 or miR-222 and SIRT1, but no direct target relationship was identified. These data demonstrate that miR-221 and miR-222 are highly expressed in PC-3 cells. Their inhibition leads to reduced cell proliferation and migration and increased apoptosis in prostate cancer cells. These effects are potentially mediated by up-regulation of SIRT1.