Megalin (gp 330) is a large cell surface receptor expressed on the apical surfaces of epithelial tissues, that mediates the binding and internalization of a number of structurally and functionally distinct ligands. In this paper we report the first detailed structural characterization of megalin-derived oligosaccharides. Using strategies based on mass spectrometric analysis, we have defined the structures of the N-glycans of megalin. The results reveal that megalin glycoprotein is heterogeneously glycosylated. The major N-glycans identified belong to the following two classes: high mannose structures and complex type structures, with complex structures being more abundant than high mannose structures. The major nonreducing epitopes in the complex-type glycans are: GlcNAc, Galbeta1-4GlcNAc (LacNAc), NeuAcalpha2-6Galbeta1-4GlcNAc (sialylated LacNAc), GalNAcbeta1-4[NeuAcalpha2-3]Galbeta1-4GlcNAc (Sd(a)) and Galalpha1-3Galbeta1-4GlcNAc. Most complex structures are characterized by the presence of (alpha1,6)-core fucosylation and the presence of a bisecting GlcNAc residue.