Background: Diabetes mellitus is linked with many macrovascular and microvascular complications including cardiovascular, neuro, eye, kidney, liver, and reproductive injuries. Both clinical and animal research disclosed deterioration of spermatogenesis, decreased sperm count, seminal fluid volume, sperm motility, and depressed testosterone concentrations during diabetes. Nanotechnology employment in the alternative medicine field is one of the rapidly rising areas. Objective: To investigate the therapeutic effect of crude, nanoparticles (NPs) Costus speciosus (C. speciosus), and metformin against type 2 diabetes. In addition, their role in treating diabetes-induced testicular toxicity was investigated. Material and Methods: Diabetes was induced by feeding the rats with a high-fat diet (HFD) for 2 weeks followed by single i.p. injection of STZ at a dose of 45 mg/kg. Two weeks after STZ injection, crude (500 mg/kg) and NPs C. speciosus (250 mg/kg) and metformin (200 mg/kg) were administered daily by gavage for a period of 8 weeks. Results: Only NPs C. speciosus significantly decreased serum glucose levels versus diabetic rats. The hypoglycemic effect of NPs C. speciosus was similar to the metformin effect and superior to crude C. speciosus. All treatment regimens significantly increased % body weight gain than diabetic rats. All regimens significantly increased serum insulin and testosterone levels. Concerning testosterone crude C. speciosus is superior to NPs C. speciosus an effect confirmed with the histopathological findings. Conclusion: A lower dose of NPs C. speciosus significantly ameliorated diabetes-induced hyperglycemia, body-weight loss, and testicular damage.