1-(Tetrahydro-2-furanyl)-5-fluorouracil (Thf-FU), which is named Ftorafur or FT-207 and is used clinically as an antitumor agent, was conveniently synthesized by condensation of the trimethylsilyl derivative of 5-fluorouracil with 2-acetoxytetrahydrofuran using NaI as a catalyst. This optically inactive Thf-FU was resolved into optically active (R)-(+)- and (S)-(-)-Thf-FU in high optical purity and excellent yield by formation of diastereoisomers with brucine. 13C NMR data were obtained on Thf-FU and related compounds and the antibacterial activities and in vivo antitumor activities of these isomers were tested. The degradations of these isomers to 5-fluorouracil by liver microsomes were also examined. No significant differences were found in any of these properties of these isomers.