Carbohydrate-protein interactions on surface and in solution were quantitatively measured by a glycan microarray. Assessing carbohydrate affinities is typically difficult due to weak affinities and limited sources of structurally complex glycans. We described here a sensitive, high-throughput, and convenient glycan microarray technology for the simultaneous determination of a wide variety of parameters in a single experiment using small amounts of materials. Assay systems based on this technology were developed to analyze multivalent interactions and determine the surface dissociation constant (K-D,K-surf) for surface-coated mannose derivatives with mannose binding lectins and antibodies. Competition experiments that employed monovalent ligands in solution yielded K-D and K-i values in solution similar to equilibrium binding constants obtained in titration microcalorimetry and surface plasmon resonance experiments.