A white rot fungus was isolated from rotted leaves and identified as Pestalotiopsis sp. KCTC 8637P. It produced a flocculant biopolymer. A flocculant was partially purified from the culture broth by series of precipitations with 95% ethanol and named as Pestan. The components of Pestan were consisted of glucose : glucosamine : glucuronic acid : rhamnose with a approximately molar ratio of 100:3.5:1.6:1.3. In kaolin suspension(final concentration was 4,800 mg/l), the highest flocculating activity was attained at tile biopolymer flocculant concentration of 1 mg/l. The flocculating activity was observed most highest by the addition of cationic solutions, especially 8mM CaCl2 . 2H(2)O or 8mM FeCl3. The thermal stability of Pestan was sustained up to 70 degrees C.