Prostate cancer is one of the most prevalent malignancies and is the second leading cause of cancer-related deaths in men. Fruit and vegetable consumption is a novel, non-toxic therapeutic approach that can be used to prevent and treat prostate cancer. Citrus peels and their extracts have been reported to have potent pharmacological activities and health benefits due to the abundance of flavonoids in citrus fruits, particularly in the peels. Our previous studies demonstrated that oral administration of Gold Lotion (GL), an extract of multiple varieties of citrus peels containing abundant flavonoids, including a large percentage of polymethoxyflavones (PMFs), effectively suppressed azoxymethane (AOM)-induced colonic tumorigenesis. However, the efficacy of GL against prostate cancer has not yet been investigated. Here, we explored the anti-tumor effects of GL using a human prostate tumor xenograft mouse model. Our data demonstrated that treatment with GL by both intraperitoneal (i.p.) injection and oral administration dramatically reduced both the weights (57%-100% inhibition) and volumes (78%-94% inhibition) of the tumors without any observed toxicity. These inhibitory effects were accompanied by mechanistic down-regulation of the protein levels of inflammatory enzymes (inducible nitric oxide synthase, iNOS and cyclooxygenase-2, COX-2), metastasis (matrix metallopeptidase-2, MMP-2 and MMP-9), angiogenesis (vascular endothelial growth factor, VEGF), and proliferative molecules, as well as by the induction of apoptosis in prostate tumors. Our findings suggest that GL is an effective anti-cancer agent that may potentially serve as a novel therapeutic option for prostate cancer treatment.