Micronucleus technique used to evaluate the degree of chromosomal damage at single cell level . Micronuclei originate from chromosome fragments or whole chromosomes that are not separated during cell division . This method is easy to use in human lymphocytes and thus suitable to conduct monitoring studies on human populations. It is now widely used to assess the effects of environmental, genetic factors and lifestyle on genetic stability . In this paper describes the basic principles underlying this method, including the method of counting and evaluation criteria for micronuclei .