Cancer-associated carbohydrate antigens are often found on the surface of cancer cells. Understanding their roles in cancer progression will lead to the development of new therapeutics and high-sensitivity diagnostics for cancers. Globo H is a member of this family, which is highly expressed on breast cancer cells. Here, we report the development of a glycan microarray of Globo H and its analogs for measurement of the dissociation constants on surface (K(D,surf)) with three different monoclonal antibodies (VK-9, Mbr1, and anti-SSEA-3), to deduce their binding specificity. The glycan microarray was also used to detect the amount of antibodies present in the plasma of breast cancer patients and normal blood donors. It was shown that the amount of antibodies against Globo H from breast cancer patients were significantly higher than normal blood donors, providing a new tool for possible breast cancer diagnosis. Compared with the traditional ELISA method, this array method required only atto-mole amounts of materials and is more effective and more sensitive (5 orders of magnitude). The glycan microarray thus provides a new platform for use to monitor the immune response to carbohydrate epitopes after vaccine therapy or during the course of cancer progression.