Mehdi Kian1, Ali Soleimanzadeh1*, Shahram Javadi2, Gholamreza Najafi3 Intra-testicular injection of Zinc Oxide Nanoparticles versus surgical castration to sterilize male rats Mehdi Kian1, Ali Soleimanzadeh1*, Shahram Javadi2, Gholamreza Najafi3 Department of Theriogenology, Faculty of Veterinary Medicine, Urmia University, Urmia, Iran Department of Internal diseases and clinical pathology, Faculty of Veterinary Medicine, Urmia University, Urmia, Iran Department of Basic Sciences, Faculty of Veterinary Medicine, Urmia University, Urmia, Iran   Objectives Rats on experimental and control groups were killed under anesthetic conditions after 30 and 60 days. sperm count, sperm motility, sperm morphology, sperm viability, DNA integrity and Teratozoospermia Index were measured. Conclusions Male sterilization by chemical agents is a nonsurgical contraceptive approach designed to induce azoospermia and, therefore, infertility. The objective of the present study was to evaluate, sperm count, sperm motility, sperm morphology, DNA integrity and Teratozoospermia Index were evaluated after intratesticular injection of Zinc Oxide Nanoparticles in rats. Low cost, ease of use, and cultural acceptance of a castration technique that does not require removal of the testes make Zinc Oxide Nanoparticles a valuable option for large-scale use in animals, particularly in remote locations lacking sophisticated clinical facilities or skilled surgeons and staff. Notably, Intratesticular injection of Zinc Oxide Nanoparticles solution impaired spermatogenesis in rats and has great potential as a permanent sterilize in this species. Results The sperm count, sperm motility, sperm morphology and sperm viability in Zinc Oxide Nanoparticles group were significantly lower than the control group (p<0.05). On the other hand, DNA integrity in Zinc Oxide Nanoparticles group was significantly higher than zinc oxide and distilled water groups (p<0.05). Also, Teratozoospermia Index was significantly increased in Zinc Oxide Nanoparticles group (p<0.05). Methods Sixty adult male Wistar rats were divided into 6 groups randomly. After 10 days of acclimation time, the animals were sedated by xylazine, ketamine cocktail. The testicle diameter related volume of Zinc Oxide Nanoparticles (with different concentrations of 5, 10 and 25 mg/ml), zinc gluconate (25 mg/ml) and sterile distilled water were injected via the intratesticular method in each group separately. Keywords: Zinc Oxide Nanoparticles, sterilize, Intra-testicular, rats