A palladium-catalyzed one-pot Tsuji-Trost type decarboxylative allylation/Wittig reaction has been developed to synthesize C-vinyl glycosides. Screening of various aldehydes led to formation of β,(E)-selective C-vinyl glycosides with pyridyl group containing aldehydes and β,(Z)-selective C-vinyl glycosides with nonpyridyl aldehydes. A plausible mechanism is proposed based on the coordination effect of the aldehydes.