A sialyl Lewis x-PEG-DSPE derivative (3) has been prepared using a combined chemical enzymatic approach and incorporated into mPEG-DSPE containing liposomes (PEG, poly(ethylene glycol); mPEG, methoxypoly(ethylene glycol); DSPE, distearoylphosphatidylethanolamine). Several liposomal formulations of 3 were evaluated as inhibitors of E-selectin mediated cellular adhesion in an ELISA assay and were found to be similar to 750-fold more potent than the nonliposomal oligosaccharide (2) and greater than 5000-fold more potent than the natural glycotope structure (1). The dramatic increase in potency of the liposomal formulations suggests that oligosaccharide multivalency enhances inhibition of E-selectin adhesion and is an effective approach to the design of more potent selectin cell adhesion inhibitors.