Although mercuric chloride has toxicity on reproductive system, it is uncertain if such toxicity is induced by estrogen-like effect. To study whether mercuric chloride has the estrogen-like effect and its relevant mechanism, proliferation assay of MCF-7 human breast cancer cells, uterotrophic assay, peroxidase activity assay and estrogen receptor competitive binding assay were conducted to screen the estrogen-like effect of mercuric chloride. The MCF-7 cells proliferated in the stimulation of mercuric chloride and got to the peak at 10(-7) mol/l concentration. And this proliferation could be completely blocked by estrogenic antagonist ICI182.780. In addition, mercuric chloride could increase the weight of uterus of ovariectomized SD rats and the peroxidase activity of uterus complying with dose-effect relationship. However, mercuric chloride could not affect the binding of estradiol (E(2)) to estrogen receptor (ER). So mercuric chloride exhibits the estrogen-like effect through binding and activating ER rather than bind to ER by competing with E(2).