Abstract: The present invention relates to a composition for preventing or treating muscle diseases, wherein the composition contains homoharringtonine as an active ingredient, wherein it was found that the suppression of a decrease in skeletal muscle mass and improved muscle strength were exhibited in an experimental group in which homoharringtonine was administered to an animal model in which reduction in muscle mass and muscular atrophy were induced by obesity, aging, or the fixing of lower extremities, and thus the composition including homoharringtonine as an active ingredient can be provided as a pharmaceutical composition or a health food for preventing or treating muscle diseases caused by a decrease in muscle mass or muscle strength.