Estramustine (INNTooltip International Nonproprietary Name, USANTooltip United States Adopted Name, BANTooltip British Approved Name) is an estrogen and cytostatic antineoplastic agent which was never marketed. It is a carbamate derivative of estradiol and acts in part as a prodrug of estradiol in the body. Estramustine phosphate, the C17β phosphate ester of estramustine and a prodrug of estramustine, estromustine, estradiol, and estrone, is marketed and used in the treatment of prostate cancer.

Estramustine is a carbamate derivative of the natural hormone, estradiol. The amine (ClCH₂CH₂)₂NH is treated with phosgene to give the acid chloride of normustine. This reacts with the phenolic hydroxyl group of estradiol in the presence of a base to give estramustine.