Titanium oxide nanoparticles with various capabilities such as high oxidation, biocompatibility, and photocatalytic features are used frequently in wide range of sciences including medicine, engineering, cosmetics production and pharmacology. Considering frequent use of titanium oxide nanoparticles, it is important to study the distribution and toxicity of it in body. The goal of this study was investigating the effects of titanium oxide nanoparticles on testis tissue of male mice. Forty male mice were divided into four groups: control group did not receive anything, placebo group, and two experimental groups which received 10 and 100ppm of nanoparticles via gavage. At the end of period testes were colored using hematoxylin eosin method and studied using light microscopy. Obtained data were analyzed using SPSS software. According to results, both 10 ppm and 100 ppm groups reduced testis stem cells and primary spermatocytes significantly which is in accordance to epididymis images. Titanium oxide nanoparticles can pass the blood-testis barrier, be accumulated in testis and damage testis. So this nanoparticle has negative effects on male sex.