The desilylation reaction of γ-silylated allylic sulfones was found to proceed through γ-silylated (E)-vinylic sulfones to afford the corresponding allylic sulfones by treatment with DBU and H2O. The Z/E ratio of the resulting allylic sulfones varied according to the γ-substituents of the γ-silylated sulfones. This stereochemical outcome was rationalized by “syn-effect.”