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Transmembrane mucins are highly -glycosylated glycoproteins that coat the apical glycocalyx on mucosal surfaces and represent the first line of cellular defense against infection and injury. Relatively low levels of -glycans are found on transmembrane mucins， and their structure and function remain poorly characterized. We previously reported that carbohydrate-dependent interactions of transmembrane mucins with galectin-3 contribute to maintenance of the epithelial barrier at the ocular surface. Now， using MALDI-TOF mass spectrometry， we report that transmembrane mucin -glycans in differentiated human corneal epithelial cells contain primarily complex-type structures with -acetyllactosamine， a preferred galectin ligand. In -glycosylation inhibition experiments， we find that treatment with tunicamycin and siRNA-mediated knockdown of the Golgi -acetylglucosaminyltransferase I gene () induce partial loss of both total and cell-surface levels of the largest mucin， MUC16， and a concomitant reduction in glycocalyx barrier function. Moreover， we identified a distinct role for -glycans in promoting MUC16's binding affinity toward galectin-3 and in causing retention of the lectin on the epithelial cell surface. Taken together， these studies define a role for -linked oligosaccharides in supporting the stability and function of transmembrane mucins on mucosal surfaces.