Anthocyanins are natural colorants, with potential chemopreventive activity. 5-Flurouracil (5-Fu) is a widely used cancer chemotherapeutic drug. However, it has serious side effects. Objective: To determine whether anthocyanin-rich-extracts (ARE) can increase the effectiveness of 5-Fu. Methods: Colon cancer cells were treated with ARE in combination with 5-Fu to assess in vitro whether ARE would enhance 5-Fu cytotoxicity. In vivo, rats were given diets with or without ARE for 14 days. On day 11, rats were injected with either 5-Fu or its vehicle. Total blood cells counts and pathological analyses were conducted. Results: ARE enhanced the growth inhibition by 5-Fu in colon cancer cell lines, but almost had no effect on normal colon cells. 5-Fu had serious side effects on the rats. Dietary ARE partially reduced the gastrointestinal damage by 5-Fu. Further studies with advanced tumor models are needed to assess effect of ARE on 5-Fu tumor inhibition in vivo.