There is very little research on the synthesis of β-3-deoxy-D-manno-oct-2-ulosonic acid (Kdo) C-glycosides, which restricted their widespread application. Herein, a convenient and efficient approach to synthesize β-Kdo C-glycosides was developed based on a Tf2O/(p-Tol)2SO preactivation strategy using bench stable peracetylated Kdo thioglycoside as a donor via a thermodynamic SN1-like mechanism.