Curcumin possesses chemopreventive properties against several types of cancer, but the molecular mechanisms by which it induces apoptosis of cancer cells and inhibits cancer cell proliferation are not clearly understood. To evaluate the antitumor activity of curcumin for prostate cancer, we used an androgen dependent LNCaP prostate cancer cell line and an androgen independent PC-3 prostate cancer cell line as experimental models. We treated these cells with curcumin and then evaluated the effects of curcumin on cell cycle profiling and apoptosis, as well as the activation of NF-kaapaB and c-jun in these cells. The results showed that the ratios of apoptosis in LNCaP and PC-3 cells were significantly elevated in a dose dependent manner after exposure to curcumin. In addition, curcumin induces the G2/M cell cycle arrest of LNCaP and PC-3 cells in a dose dependent manner. Mechanistically, we found that curcumin upregulated the protein level of NF-kappaB inhibitor IkappaBalpha and downregulated protein levels of c-Jun and AR. These data suggest that curcumin is a promising agent for the treatment of both androgen-dependent and androgen-independent prostate cancer.