Abstract: Estradiol conjugate has been used as a tracer to detect estrogen receptor of human mammary cancer cells. In order to look for more stable carrier of fluorescent estradiol conjugate, we substituted polyethyleneglycol (PEG) for bovine serum albumin (BSA) and synthsized 17β-estradiol- 6- carboxymethyl- oxime- PEG-fluorescein isothiocyanate. The structure of the title compound was confirmed by IR and UV. In this paper, we also discribe another procedure to convert the terminal hydroxyl groups of PEG to the more reactive primary amino PEG by tosylation, azide group substitution and catalytic hydrogenation. The ratio of conversion is about 87%.