The aim of this study is to determine radio protective effect of royal jelly on ionizing radiation-induced DNA damage in human peripheral blood lymphocytes. In this quasi experimental study, men at the age of 20 to 45 year old would attend. All participants with a history of radiotherapy, chemotherapy and allergy to royal jelly would be excluded. 30 men admitted to Hazrat-e- Maryam fertility center would participate in our study. In this study each participant gives blood samples twice. First sampling, on admission to the fertility center. After first sampling each participant would start taking orally 1000 mg royal jelly per day for two weeks. Second sampling would happen after this period. In each sampling step, blood samples would be divided into two parts, pre-irradiated and post-irradiated, and all of them would be investigated regarding DNA damage by Comet Assay. Primary outcome measures are DNA tail length.