Recently, studies have investigated the significance of the Wnt/β-catenin pathway in prostate cancer. The transcriptional activity of the androgen receptor (AR) is modulated by interaction with coregulators, one of which is β-catenin. Curcumin, a dietary yellow pigment of Curcuma longa, has emerged as having a chemopreventive role. Although curcumin has been shown to inhibit AR expression, its molecular mechanism has not been fully elucidated. In this study, whether curcumin mediates the Wnt/β-catenin signaling pathway with regard to AR/β-catenin interactions was studied. Curcumin was shown to induce significant inhibition of AR expression in a dose-dependent manner. Marked curcumin-induced suppression of β-catenin was shown in the nuclear and cytoplasmic extracts as well as whole cell lysates. Further analysis revealed that phosphorylation of Akt and glycogen synthase kinase-3β were attenuated, but phosphorylated β-catenin was increased after curcumin treatment. Finally, cyclin D1 and c-myc, the target gene of the β-catenin/T-cell factor transcriptional complex, were also decreased. These findings suggest that curcumin modulates the Wnt/β-catenin signaling pathway and might have a significant role in mediating inhibitory effects on LNCaP prostate cancer cells.