Background: Nanoparticles due to their small size can overcome blood-testis barrier and affect spermatogenesis process. The aim of this study is to investigate the influence of trioxide (MoO3) nanoparticles on histological changes of testis and spermatogenesis process in adult male Wistar rats.

Materials and Methods: In this experimental study 30 adult male Wistar rats were randomely divided into five groups (n=6), including control, 2 sham groups, and 2experimental groups. Control group had no treatment. Two experimental groups received doses 5 & 10 mg/kg/BW nano molybdenum trioxide (20nm) respectively, and two sham groups received the same doses of normal saline by intraperitoneal injection. After 28 days, rats testis was removed and fixed in Bouin’s fixative for histological examination. The 5&mum sections were stained with hematoxilin-eosin.

Results: In experimental group which received 5mg/kg/BW nanoparticle, there was some disorganization of spermatogenic cells in some seminiferous tubules. In experimental group which received 10mg/kg/BW nanoparticle, a significant decrease was also observed in the number of spermatogenic and sertoli cells in comparison with the control group.

Conclusion: According to the findings of this study exposure to the high doses of (MoO3) nanoparticles can disrupt male reproductive system in a dose- dependent manner. Hence, the application of (MoO3) NPs should be carried out cautiously.