This work was designed to evaluate the role of selenium nanoparticles loadedonMoringa oleifera leaves extract (MOLE-SeNPs conjugate) on the testicular toxicity induced by melamine in rats. Forty male Albino rats of 10 weeks old were assigned to four groups; control group, group 2; SeNPs group (0.5 mg/kg BW orally) for 6 weeks, group 3; melamine (800 mg/kg BW orally) for 6 weeks and group 4; melamine followed by MOLE-SeNPs conjugate (200 mg/kg BW orally) for 6 weeks. Reproductive parameters; sex steroid hormonal level, molecular analysis of the transcriptional levels of steroidogenic enzymes and testicular histopathology were evaluated. In the melamine (MA) group, significant decrease in the semen quality, testicular weight, gonadosomatic index, FSH, LH, free testosterone and total testosterone were detected in comparison to the control group, however, estradiol (E2) level was significantly elevated )187.45%) in comparison to the control group. These parameters were significantly reversed in the MOLE-SeNPs conjugate group. Moreover, a significant decrease (45.21% and 23.75%) was detected in steroidogenic enzyme genes (CYP11A1 and HSD17B3) in the MA group than in the control one (P < 0.05). However, the transcriptional level of aromatase gene (CYP19A1) showed a significant increase (171.28%) in testicular tissue in comparison to the control group. The MO-SeNPs conjugate treatment increased the expression of CYP11A1 and HSD17B3 genes in testicular tissue but the transcriptional level of aromatase gene (CYP19A1) showed a significant decrease in comparison with the melamine group. The levels of testicular antioxidant enzymes (superoxide dismutase, catalase, and glutathione peroxidase) showed a significant decrease in the MA group than the control group. These changes were meaningfully increased in the MO-SeNPs conjugate treated group in comparison to the melamine group. Histopathologically, the testicular tissue indicated improvement of injury in the concurrent MA+ MO-SeNPs conjugate group in comparison to MA group. In conclusion, MO-SeNPs conjugate can ameliorate the toxic impacts of melamine on testicular tissue in rats mainly via affecting the steroidogenic pathway.