The estrogenicity of parabens at human exposure levels has become a focus of concern due to the debate over whether the estrogenicity of parabens is strong enough to play a role in the increased incidence of breast cancer. In this study, the uterotrophic activities of methylparaben (MP) and ethylparaben (EP) at doses close to the acceptable daily intake as allocated by JECFA were demonstrated in immature Sprague-Dawley rats by intragastric administration, and up-regulations of estrogen-responsive biomarker genes were found in uteri of the rats by quantitative real-time RT-PCR (Q-RT-PCR). At the same time, the urinary concentrations of MP and EP, as measured by gas chromatography-mass spectrometry (GC-MS) in rats that received the same doses of MP and EP, were found to be near the high urinary levels reported in human populations in recent years. These results show the in vivo estrogenicity of MP and EP at human exposure levels, and indicate that populations exposed to large amounts of MP and EP may have a high burden of estrogenicity-related diseases. In addition, a molecular docking simulation showed interaction between the parabens and the agonist-binding pocket of human estrogen receptor α (hERα).