Prostate cancer is one of the leading causes of cancer death in men in Western countries. Epidemiological studies have linked the consumption of fruits and vegetables to a reduced risk of prostate cancer, and small fruits are particularly rich sources of many active phytochemical stilbenes, such as pterostilbene. As a constituent of small fruits such as grapes, berries, and their products, pterostilbene is under intense investigation as a cancer chemopreventive agent. Using the p53 wild type LNCaP and p53 null PC3 cells, we found that treatment with pterostilbene resulted in dose-dependent inhibition of cellular proliferation, which suggested that the interaction of pterostilbene with the p53 might not fully explain its inhibitory effect on proliferation. In this study, we found that pterostilbene activated AMPK in both p53 positive and negative human prostate cancer cells. Pterostilbene-activated AMPK decreased the activity and/or expression of lipogenic enzymes, such as fatty acid synthase (FASN) and acetyl-CoA carboxylase (ACC). Interestingly, the resolution between apoptosis and growth arrest following AMPK activation is greatly influenced by p53 status. In p53 positive LNCaP cells, pterostilbene blocked the progression of cell cycle at G1 phase by inducing p53 expression and further up-regulating p21 expression. However, pterostilbene induced apoptosis in p53 negative PC3 cells. Our results suggest that pterostilbene may be a functional chemopreventive agent and that dietary exposure to pterostilbene would be helpful for antiprostate cancer activity.