Considerable evidence in recent years suggests that garlic has anti-proliferative effects on various types of cancer. Garlic contains water-soluble and oil-soluble sulfur compounds. Oil-soluble compounds (OSCs), such as diallyl sulfide (DAS), diallyl disulfide (DADS), diallyl trisulfide (DATS) and ajoene are more effective than watersoluble compounds in protection against cancer. DADS, a major organosulfur compound derived from garlic, can reduce carcinogen-induced cancers in experimental animals and inhibit the proliferation of various types of cancer cells. The mechanisms of these action of DADS include activation of metabolic enzymes that detoxify carcinogens, suppression of the formation of DNA adducts, antioxidant effects, regulation of cell-cycle progression, induction of apoptosis, and inhibition of angiogenesis and metastasis. These topics are discussed in depth in this review.