Background Silymarin (SMN) is a natural component polyphenolic purified from Silybum marianum (milk thistle) seeds. SMN can control reactive oxygen species and converts them into compounds with minimizing their toxicity. Objectives The aim of the present study was to evaluate the therapeutic effect of silymarin nanoparticles on sperm parameters of rats induced diabetes by alloxan. Methods: Firstly gas liquid chromatography (GCMS) was utilized to identification active compound in milk thistle, then the preparation of silymarin -TPGS nanoparticles: Nanoparticles of silymarin of were prepared by the Nano precipitation. Forty Wistar albino rats were divided into four groups, control, induced diabetic with 150mg/kg of alloxan I.p, group three and four induced diabetic and treated with milk thistle extract and nanoparticles at a dose of 100 mg/kg.bw daily orally, for 60 days, Blood was collected from heart puncture for estimate serum FSH, L.H, and testosterone, then animal sacrificed to evaluate sperm quality and quantity as well as the histopathological section of tests. Results: Biochemical inspection appear that SMN nanoparticles improved sperm quality and quantity when compared with untreated and SMN groups. SMN nanoparticles appear to have therapeutic effects as an antioxidant against alloxan-induced damage in rat testes. Conclusions: Silymarin nanoparticles can be considered as a hopeful herbal as complementary medicine which may play a significant role to save normal spermatocytes against ROS effects-induced reproductive damage.