Endocrine modulating effects of Simvastatin (SV) and its metabolite, Simvastatin β-hydroxy acid (SVA), were investigated in H295R cells and in female Sprague-Dawley (SPRD) rats. H295R cells were exposed to SV and SVA concentrations from 0 to 10μM for 48h. Four groups of SPRD rats received 0 (CT), 1.3 (L), 5.0 (M), and 20.0 (H)mg SV/kg bw/day for 14 days. 10 Steroids were investigated in H295R growth media, and in tissues and plasma from rats using GC-MS/MS. Plasma LH and FSH were quantified by ELISA. In the H295R assay, SV and SVA particularly decreased progestagens with IC50-values from 0.10-0.13μM for SV and from 0.019-0.055μM for SVA. In rats, SV decreased progestagens in ovaries, brain and plasma, and plasma FSH in the M (72.4% decrease) and H group (76.6% decrease). Because progestagens and gonadotropins are major players in fertility, administration of SV might exert negative effects on female reproduction.