Sweet potato (Ipomoea batatas) leaves or greens, extensively consumed as a vegetable in Africa and Asia, are an excellent source of dietary polyphenols such as anthocyanins and phenolic acids. Here, we show that sweet potato greens extract (SPGE) has the maximum polyphenol content compared with several commercial vegetables including spinach. The polyphenol-rich SPGE exerts significant antiproliferative activity in a panel of prostate cancer cell lines while sparing normal prostate epithelial cells.