RP215 monoclonal antibody was shown to react with carbohydrate-associated epitope(s) in cancer cell-expressed glycoproteins known as CA215 based on indirect experimental evidences. Efforts have been made to identify glycans in CA215 that may be involved in the epitope recognition. More than 100 tryptic peptides, derived from affinity-purified CA215, consist mainly of immunoglobulin superfamily (IgSF) proteins (~60%), mucins (~7%), and others. Glycoanalysis was performed with affinity-purified CA215 from two cancer cell lines, including (1) N- and O-linked glycan profilings and linked glycoanalysis, (2) glycosylation site mappings, and (3) treatments with selected glycolytic enzymes. High mannose and complex bisecting structures with terminal sialic acid (NeuAc or NeuGc) were detected in N-glycans, whereas as many as 10 O-glycans structurally similar to those of mucins were identified. Through glycosylation site mappings, two N-linked and six out of eight O-linked glycans were detected and matched almost 100% with human immunoglobulin heavy chains. Treatments with several glycolytic enzymes were found to have little effect on the immunoactivity of the RP215-epitope. The same activity was also not affected by the cancer cell culture in human serum instead of bovine serum, indicating that NeuAc and NeuGc are not involved in epitope recognition. The immunoassay results also suggested that the affinity-purified cancer cell-expressed immunoglobulins revealed similar structures and immunoactivities to those of normal human immunoglobulins, except that two additional O-glycans were detected in the former. Supplemental materials are available for this article. Go to the publisher's online edition of Journal of Carbohydrate Chemistry to view the free supplemental file.