A new multivalent glycopolymer platform for lectin recognition is introduced in this work by combining the controlled growth of glycopolymer brushes with highly specific glycosylation reactions. Glycopolymer brushes, synthetic polymers with pendant saccharides, are prepared by surface-initiated atom transfer radical polymerization (SI-ATRP) of 2-O-(N-acetyl--d-glucosamine)ethyl methacrylate (GlcNAcEMA). Here, the fabrication of multivalent glycopolymers consisting of poly(GlcNAcEMA) is reported with additional biocatalytic elongation of the glycans directly on the silicon substrate by specific glycosylation using recombinant glycosyltransferases. The bioactivity of the surface-grafted glycans is investigated by fluorescence-linked lectin assay. Due to the multivalency of glycan ligands, the glycopolymer brushes show very selective, specific, and strong interactions with lectins. The multiarrays of the glycopolymer brushes have a large potential as a screening device to define optimal-binding environments of specific lectins or as new simplified diagnostic tools for the detection of cancer-related lectins in blood serum.