Abstract: The level of progesterone receptors (PR) in breast tumors can be used to guide the endocrine therapy of breast cancer. As the tanaproget analogue, 5-［4-(3-fluoro-propyl)-4-methyl-2-oxo-1,4-dihydro-2H-benzo［d］［1,3］oxazin-6-yl］-1H-pyrrole-2-carbonitrile (¹⁹FPr-Tanaproget) is a nonsteroidal progesterone receptor agonist with very high PR binding affinity and high selectivity. Radiolableled with fluorine-18, it might be used to image PR-positive breast tumors by positron emission tomography (PET). The nonradioactive ¹⁹FPr-Tanaproget and radioactive 18FPr-Tanaproget were synthesized. Crude ¹⁸FPr-Tanaproget was separated by Sep-Pak C-18 and semi-preparative HPLC, respectively. The results show that the radiochemical purity is over 97%. It is very stable in vitro within 6h in saline and serum incubation. The factors influencing labeling efficiency were investigated. The results indicate that the optimal preparation conditions are as follows: the reaction temperature is 100℃; the reaction time is 35 min; and the concentration of precursor is 32.7 mmol/L. Under this condition, the total synthesis time is 45 min, and the corrected radiochemical yield can achieve to 10.9%.