Cancer prevention by vegetable diet has received considerable attention in recent years. In the past these attributes of vegetables were based more on beliefs than on scientific evidences. But over the past few decades many studies have been performed about that. Cancer preventive components of many vegetables have been studied in experimental carcinogenesis models. These studies have reported on these components influence carcinogenesis during initiation and promotion phases of cancer development. Also, epidemiological studies and clinical trials have reported cancer preventive effects of vegetables. However, there is no comprehensive summary of cancer preventive effects with the types of vegetables. In this review, we classified the vegetables and described the mechanism of action of active components of vegetables, experimental studies, and clinical trials. Results revealed a negative correlation between consumption of vegetables and cancer risk. But we can't still conclude the effects of vegetables yet, so further studies would be necessary for final conclusion.