Angiogenesis is an essential step in initial tumor development and metastasis. Consequently, compounds that inhibit angiogenesis would be useful in treating cancer. A variety of antitumor effects mediated by 1alpha, 25-dihydroxyvitamin D3 (1,25-VD) have been reported, one of which is anti-angiogenesis; however, detailed mechanisms remain unclear. We have demonstrated that 1,25-VD inhibits prostate cancer (PCa) cell-induced human umbilical vein endothelial cell migration and tube formation, two critical steps involved in the angiogenesis. An angiogenesis factor, interleukin-8 (IL-8), secreted from PCa cell was suppressed by 1,25-VD at both mRNA and protein levels. Mechanistic dissection found that 1,25-VD inhibits NF-kappaB signal, one of the most important IL-8 upstream regulators. The 1,25-VD-mediated NF-kappaB signal reduction was shown to result from the blocking of nuclear translocation of p65, a subunit of the NF-kappaB complex, and was followed by attenuation of the NF-kappaB complex binding to DNA. The role of IL-8 in PCa progression was further examined by PCa tissue microarray analyses. We found that IL-8 expression was elevated during PCa progression, which suggests that IL-8 may play a role in tumor progression mediated through its stimulation on angiogenesis. These findings indicate that 1,25-VD could prevent PCa progression by interrupting IL-8 signaling, which is required in tumor angiogenesis, and thus applying vitamin D in PCa treatment may be beneficial for controlling disease progression.