A glycosphingolipid analogue (12-azidododecyl beta-lactoside) as a saccharide primer has been shown to be useful for the synthesis of oligosaccharide libraries by mammalian cells. In the present study, CE-ESI-MS was employed to elucidate the structure of glycosphingolipid analogues derived from 12-azidododecyl beta-lactoside (Lac-C12N3) by mammalian cells. MDCK cells and COLO201 cells were cultured with Lac-C12N3, and the glycosylated products secreted into the medium were collected and separated into acidic and neutral products by column chromatography. The acidic products could be directly analyzed by CE-ESI-MS, while the neutral products were converted to anionic derivatives via a reaction with propiolic acid. With this method, it was possible to analyze both acidic and neutral products glycosylated by MDCK cells and COLO201 cells at high sensitivity.