In the coccolithophorid microalgae acidic polysaccharides are considered to be involved in the formation of the calcified scale, coccolith. Characteristics of the acidic polysaccharides extracted from the cell surface of the coccolithophorid Pleurochrysis haptonemofera were analyzed. The acidic polysaccharides on the cell surface can be detected by measuring fluorescence of cells after fluorescein-isothiocyanate-labeled lectin staining by flow cytometry. Flow cytometric analyses revealed that the acidic polysaccharides remained on the cell surface even after CaCO3 in the coccolith was dissolved by lowering pH, but they were extracted by subsequent EDTA or EGTA treatment, suggesting that they are bound not into the CaCO3 crystals of the coccolith, but onto the surface via Ca2+. Analyses of the acidic polysaccharides by anion exchange chromatography, colloidal precipitation with divalent cations, and polyacrylamide gel electrophoresis (PAGE) revealed that P. haptonemofera has 3 types of acidic polysaccharides (Ph-PS-l, -2, and -3). The PAGE patterns suggested that Ph-PS-2 has a repeated structure with a broad range of molecular weight, as in Pleurochrysis carterae, while Ph-PS-1 and -3 contain several minor components in addition to a major component, respectively. The minor components in Ph-PS-1 and -3 that have not been found in P. carterae might be characteristic of P. haptonemofera. Analyses of both the cell surface treated by various concentrations of EDTA and EGTA and the extracts suggested that Ph-PS-2, which is distinguishable by a higher affinity to concanavalin A, is bound onto the coccolith surface more intensely than the other two types of acidic polysaccharides.