The coccolithophorids have calcified scales called coccoliths on their surface that include abundant acid polysaccharides. To determine the localization and associative strength of acid polysaccharides Ph-PS-1, -2, and -3 incoccoliths of Pleurochrysis haptonemofera, we analyzed the acid polysaccharides extracted with urea from partially decalcified coccoliths. On treatment of coccoliths with8.0 Murea at pH8.0 inboiling water, Ph-PS-2 was not extracted, but parts of Ph-PS-1 and -3 were from the surface without the crystal morphology being affected. When coccoliths were partially decalcified at various pHs (pH 8.0 - 5.0), Ph-PS-1, -3, and -2 were extracted with urea in that order as the calcite crystals dissolved. Detection of the acid polysaccharides using fluorescein-isothiocyanate-labeled lectin (ConA) and anti-Ph-PS-2 antibodies demonstrated that Ph-PS-2 exists on the surfaces of both untreated and urea-treated coccoliths. Moreover, NaClO-treatment under moderate conditions extracted only Ph-PS-1, -3, and part of Ph-PS-2 from coccoliths, without separation of the crystal units, suggesting that at least some part of Ph-PS-2 acts as a glue connecting crystal units and/or a crystal unit and a base plate inside coccoliths. These results suggest that Ph-PS-2 exists not only on the surface but also inside of the coccoliths, most of it being strongly bound to coccoliths, while Ph-PS-1 and -3 are weakly associated close to the coccolith surface, in that order from the surface. This strongly supports a scheme in which PS-2 type acid polysaccharides play an important role in the crystal nucleation and PS-3 type functions during crystal growth.