Abuse of anabolic androgenic steroids (AASs) by athletes has been increased rapidly in many countries to improve their physical fitness and appearance. The abuses of AASs have been associated with impacts on different systems of the body. The present study was conducted to evaluate the histological changes that occurred in skeletal and cardiac muscles during nandrolone (one of AASs) treatment histologically and immunohistochmically. Forty adult male albino rats were divided into four groups. Group 1; control group, group 2; was treated with nandrolone 5 mg/kg intramuscularly weekly, group 3 was treated with nandrolone10 mg/kg intramuscularly weekly and group 4; was treated with nandrolone 20 mg/kg intramuscularly weekly. All groups were treated for 8 weeks. The specimens from the cardiac and skeletal muscles were processed for histological study using light and electron microscopes and immunohistochemical stain for detection of activated caspase-3 as an indicator for apoptotic changes. The skeletal and cardiac muscles appeared hypertrophied after nandrolone treatment. Lesions ranged from mild to severe muscular changes were also detected depending on the dose. The changes were in the form of variations of fibers size and splitting of some fibers in skeletal muscle as well as myofiber lysis, cellular infiltration, vacuolation, swelling and mitochondrial damage in both skeletal and cardiac muscles. The nuclei appeared hyperchromatic with peripherally clumped chromatin. Expression of caspase-3 was significantly increased in skeletal and cardiac tissues treated with higher doses of nandrolone. It is concluded that nandrolone injection in male albino rats induced hypertrophy and degenerative changes in the skeletal and cardiac muscles which may lead to loss of their functions.