There has been a renewed interest to the application of natural products derived from cruciferous plants and members of Allium genus in chemoprevention of cancer. The potential chemopreventive properties of these vegetables have been attributed to the presence of high level of organosulfur compounds in these plants. Organosulfur compounds have been shown to exert diverse biological effects such as: (a) induction of carcinogen detoxification, (b) inhibition of tumor cell proliferation, (c) antimicrobial effect, (d) free radical scavenging, (e) inhibition of DNA adduct formation, (f) induction of cell cycle arrest and induction of apoptosis etc. It has been suggested that these compounds act as chemopreventive agents through a combination of above mechanisms. Epidemiological and experimental carcinogenesis provides overwhelming evidence to support the claim that individuals consuming diet rich in organosulfur are less susceptible to different types of cancers. The protective effects of OSCs against carcinogenesis have been shown in stomach, esophagus, mammary glands, breast, skin and lungs of experimental animals. Cumulatively all these studies show a strong correlation between cancer prevention and intake of organosulfur compounds in one form or the other. Since the protective effects of all these phytochemicals are as a result of additives and synergistic combination further studies are warranted for complete understanding of chemopreventive action of organosulfur compounds and define the effective dose that has no toxicity in humans. In this review an attempt has been made to summarize the different aspects of organosulfur compounds with relation to their source, chemopreventive mechanistic action, epidemiologic and experimental carcinogenesis.