We report the first attempt of double-spot structural modification on a side-chain moiety of sulfonium-type α-glucosidase inhibitors isolated from genus <i>Salacia</i>. A series of sulfonium salts with benzylidene acetal linkage at the C3' and C5' positions were designed and synthesized. In vitro enzyme inhibition evaluation showed that compounds with a strong electron-withdrawing group attached at the <i>ortho</i> position on the phenyl ring present stronger inhibitory activities. Notably, the most potent inhibitor <b>21b</b> (1.0 mpk) can exhibit excellent hypoglycemic effects in mice, which can still compete with those of acarbose (20.0 mpk). Molecular docking of <b>21b</b> demonstrated that besides conventional interacting patterns, the newly introduced benzylidene acetal moiety plays an important role in anchoring the whole molecule in a concave pocket of the enzyme. The successful identification of <b>21b</b> as a lead compound for new drug discovery may provide a means for structure modification and diversification of the distinguished sulfonium-type α-glucosidase inhibitors.