Background & Aim: Cancer is the uncontrolled growth and spread of cells. No single causal factor stands out for cancer. Recently, diet as a probably most important factor in the etiology of cancer attracted more interests. Herbs contain many biologically active compounds that have been used extensively in herbal medicine and preparing human drugs. Many of people perceived that herbal medicine is always safe and do not have any side effects, only due to its “natural” origin. In this review we introduced a number of natural carcinogens in herbal medicine on the basis of IARC (International Agency for Research on Cancer) categories.
 Material and Methods: A literature search was conducted through PubMed, Sciencedirect and WHO΄s websites. Herbal medicine and cancer, natural carcinogen, food and cancer were used as key words. Ultimately, 39 articles were used for this review.                                                                                        
Results: A number of biochemicals that exist naturally in foods such as pirolizidin alkaloids, safrole, Anthraquinone, Aristilochic Acid, Agaritine, Cycasin, Ptaquilosid could be carcinogenic.
 Conclusion: Many bioactive compounds with known effects on human physiology and disease have been identified through studies of plants used in traditional medicine. Although most of them have health benefits but some of them can be converted to reactive intermediates causing toxicity and carcinogenicity.