An efficient synthetic strategy has been developed for the synthesis of a pentasaccharide repeating unit of the O-antigen of Escherichia coli O102 strain. The target pentasaccharide 1 has been synthesized using a [2+3] block glycosylation strategy. All glycosylation steps are highly stereoselective and high yielding. Concept of armed-disarmed and orthogonal glycosylation strategies has been applied during the synthesis. The target compound has been synthesized using the minimum number of steps.