The isoflavonoids comprise a group of phyto-oestrogens that have useful biological activities including oestrogenic, antioxidant and anticancer. As dietary components for humans, they are bioavailable from leguminous vegetables (such as genistein from soybean), and have been well-documented to have numerous health benefits. A wide range of epidemiological studies in humans and limited studies in animals have identified isoflavonoids as potential chemopreventive agents against hormone-dependent cancers. Therefore, an attempt has been made through this review to summarise the information in the mechanisms aspect of isoflavonoid phyto-oestrogens in inhibiting cancer in vitro and in vivo in the models of human cancers.