The effects of phenylthio group at C-2 of 2,3-dideoxyribose were examined for the stereoselectivities in condensation reactions between sugars and pyrimidine bases. In the case of mono-PhS sugar, the 1,2-trans-anomers were mainly obtained in the ratio of 9:1. Condensation reactions with di-PhS-sugar gave the anomeric mixtures of alpha:beta = 2:8.