Thimerosal is a compound centered on ethyl mercury which has been remained a component of vaccines. Vaccines and other medicinal product that hold thimerosal are the potential basis of relevance of havoc mercury. In the current study, the effects of thimerosal were checked on the sex hormones in adult albino rats at low 15mg/kg and high 40 mg/kg dose per day by the use of gavage for a month. Testosterone was noticeably reduced (p < 0.05) in both low and high dose treated rats. Concentration of LH and FSH also decreased (p < 0.05) tremendously in both treated groups. However, a minor decrease was observed in the level of prolactin in low dose group while prolactin was found to be reduced significantly (p < 0.05) in high dose exposure. Daily sperm production and efficiency of sperm production was also checked in this study and both are lowered sharply (p < 0.05) in rats treated with thimerosal. These results demonstrated that thimerosal has strong effects on male sex hormones and their DSP and efficiency of DSP in adult albino rats.