Prostate cancer is one of the most frequently diagnosed cancers among men. Dietary intake of nutrients is considered crucial for preventing the initiation of events leading to the development of carcinoma. Many dietary compounds have been considered to contribute to cancer prevention including zinc, which has a pivotal role in modulating apoptosis. However, the mechanism for zinc-mediated prostate cancer chemoprevention remains enigmatic. In this study, we investigated the therapeutic effect of zinc in prostate cancer chemoprevention for the first time. Exposure to zinc induced apoptosis and resulted in transactivation of p21(WAF1/Cip1) in a Smad-dependent and p53-independent manner in prostate cancer cells. Smad2 and PIAS1 proteins were significantly upregulated resulting in dramatically increased interactions between Smad2/4 and PIAS1 in the presence of zinc in LNCaP cells. Furthermore, it was found that the zinc-induced Smad4/2/PIAS1 transcriptional complex is responsible for Smad4 binding to SBE1 and SBE3 regions within the p21(WAF1/Cip1) promoter. Exogenous expression of Smad2/4 and PIAS1 promotes zinc-induced apoptosis concomitant with Smad4 nuclear translocation, whereas endogenous Smad2/4 silencing inhibited zinc-induced apoptosis accompanying apparent p21(WAF1/Cip1) reduction. Moreover, the knockdown of PIAS1 expression attenuated the zinc-induced recruitment of Smad4 on the p21(WAF1/Cip1) promoter. The colony formation experiments demonstrate that PIAS1 and Smad2/4 silencing could attenuate zinc apoptotic effects, with a proliferation of promoting effects. We further demonstrate the correlation of apoptotic sensitivity to zinc and Smad4 and PIAS1 in multiple cancer cell lines, demonstrating that the important roles of PIAS1, Smad2, and Smad4 in zinc-induced cell death and p21(WAF1/Cip1) transactivation were common biological events in different cancer cell lines. Our results suggest a new avenue for regulation of zinc-induced apoptosis, and provide a model that demonstrates zinc endorses the Smad2/4/PIAS1 complex to activate the p21(WAF1/Cip1) gene that mediates apoptosis.