ABSTRACT: Guava is fruit of Psidium guajava, and can be consumed with fresh or processed form. In this study, the antioxidant capacities and total phenolic content of guava peel, flesh and seed were evaluated using ferric reducing antioxidant power (FRAP) and Trolox equivalent antioxidant capacity (TEAC) assays as well as the Folin–Ciocalteu method, respectively. In addition, the antiproliferative capacities of guava peel, flesh and seed on four cancer cell lines, A549 (human lung cancer cells), MCF-7 (human breast cancer cells), HepG2 (human hepatoma cells) and HT-29 (human colon cancer cells) were evaluated by the MTT assay. The results showed that guava possesses strong antioxidant and anticancer actions. Furthermore, several compounds, catechin, galangin, homogentisic acid, gallic acid, kaempferol and cyanidin 3-glucoside, were identified as active components of guava, and the contents of these compounds in guava peel and seed were higher than that in guava flesh. The results suggest that guava could be developed to functional food for prevention of some diseases.