We have developed a fully automatic method for the synthesis of 16α-[ 18 F]fluoroestradiol ([ 18 F]FES) using a disposable cassette system and conventional [ 18 F]FDG module. [ 18 F]FES was synthesized using a GE TracerLab MX module and a modified module control program. Following [ 18 F]fluorination, we hydrolyzed the product three times with a mixture of 2N HCl and CH 3 CN. After HPLC purification, the decay corrected radiochemical yield of [ 18 F]FES was 45.3±2.8%, which was stable to 98.2±0.2% at 6h after synthesis. This new automated synthesis method provides high and reproducible yields with the advantage of a disposable cassette system.