Our previous study indicated that maternal high-estrogen environment in the first trimester is correlated with increased risks of low birth weight (LBW) and adult diseases. The present study aimed to establish an animal model to confirm such an effect in mice, and to further explore the mechanism involved. A mouse model with high estradiol (E₂) exposure during early pregnancy was established, and the birth weight, growth after birth, and expression levels of insulin-like growth factor-binding protein 1 (IGFBP1) of pups were examined. Meanwhile, IGFBP1 expression after treatment of E₂ was examined in a HepG2 hepatoma cell line. We found that after exposure to a high-E₂ environment the weight of the pups decreased significantly, not only before but also after birth. Meanwhile, both mRNA and protein expressions of IGFBP1 were elevated in placenta and liver tissues. Furthermore, the level of IGFBP1 in the HepG2 cell line was elevated by the treatment of E₂, whereas this effect was blocked by estrogen receptor antagonist ICI 182780. In summary, maternal high estrogen up-regulates expression of IGFBP1 in placenta and fetal livers, which contributes to LBW and decreases body weight in offspring.