Anabolic-androgenic steroids are used at high doses by athletes for improving athletic ability, physical appearance and muscle mass. Unfortunately, the abuse of these agents has significantly increased. It has been established that exercise and high doses of anabolic-androgenic steroids may influence the hypothalamic-pituitary-gonadal axis, which can in turn affect testicular apoptosis. However, the effect of the combination of exercise and high dose of anabolic-androgenic steroids on testicular apoptosis is not known. We investigated the combined effects of exercise and high doses of nandrolone decanoate on apoptosis in the spermatogenic cell lineage. Five groups of male Wistar strain albino rats were treated as follows for 8 weeks: solvent of nandrolone decanoate (peanut oil) as a vehicle (Sham); nandrolone decanoate (10 mg⁄kg⁄weekly) (nandrolone decanoate); exercise (1 hr⁄day, 5 days a week) (exercise); nandrolone decanoate (10 mg⁄kg⁄weekly) and exercise (1 hr⁄day, 5 days a week) (nandrolone decanoate exercise); and sedentary control without any injection or exercise (Control). Apoptosis in the male germ line was characterized by TUNEL, caspase-3 assay and transmission electron microscopy. The weights of the testis and accessory sex organs, as well as sperm parameters significantly decreased in the experimental groups relative to the sham and control groups (p ≤ 0.05). Germ cell apoptosis and a significant decrease in the number of germ cell layers in nandrolone decanoate exercise-treated testes were observed (p ≤ 0.05). Exercise training seems to increase the extent of apoptotic changes caused by supraphysiological dose of nandrolone decanoate in rats, which in turn affects fertility.