Curcumin is a natural polyphenol product derived from the rhizome of the Curcuma longa. In vivo and in vitro studies have uncovered many important bioactivities of curcumin, such as antioxidant activity, inducing cell apoptosis, inhibiting cell proliferation, anti-cell adhesion and motility, anti-angiogenesis and anti-microbe properties. Based on these functions, curcumin has been used in clinical trials on various inflammatory diseases and cancers. In the future, it will be necessary to focus attention partly on the clinical application of curcumin in neurodegenerative diseases, cardiovascular diseases and diabetes, because many experiments have clarified the potential value of curcumin in these areas. As a diet-derived agent, curcumin has no severe toxicity except for minor gastrointestinal side effects even up to the dosage of 8 grams for 3 months. However, curcumin has a low systemic bioavailability, so it is imperative to improve the bioavailability of curcumin in its clinical application. Many methods, such as adjuvant drug delivery system and structural modification have been demonstrated to have a potential effect.