Ganoderma lucidum is a medicinal fungus with a variety of biological activities and is used for the treatment of various diseases, including cancers. The present work is focused on the radioprotective property of G. lucidum in Swiss albino mice. Whole-body exposure of the mice to gamma radiation results in damage to cellular DNA in various tissues, such as brain, bone marrow, blood and intestine, and prior administration of a hydroal-coholic extract of G. lucidum prevented radiation-induced DNA damage. Administration of the extract prior to whole-body exposure to a lethal dose of gamma radiation gave survival advantage to mice. Also, there was considerable protection from radiation-induced loss of body weight in animals administered with the extract. The results are suggestive of the radioprotective activity of G. lucidum Extract (GLE) in mammalian organism.