Non-genomic effects of estrogen exist largely in female reproductive system. Through genomic and non-genomic pathways, and their integration, estrogen performs different physiological functions in various target tissues. In the ovary, estrogen functions as a reactive oxygen scavenger and protects ovarian cells from apoptosis through non-genomic pathway. Estrogen also regulates the expression of uterine genes in an estrogen receptor-independent manner. The review on estrogen non-genomic effects will be beneficial for understanding the mechanism of estrogen action.