Pb2+ adsorption by the living cells of the cyanobacterium Gloeocapsa gelatinosa was studied. Cyanobacterial cells with intact capsular polysaccharide (CPS) showed 5.7 times higher Pb adsorption capacity than that of cells without CPS. The adsorbed Pb was desorbed by EDTA, indicating that Pb2+ adsorption occurred mainly on cell surface. Production, sugar content and ability of CPS to remove Pb2+ were then studied in details. CPS production by G. gelatinosa increased when culture time was prolonged. The maximum CPS production was 35.43 mg g(-1) dry weight after 30-day cultivation. Xylose, arabinose, ribose, rhamnose, galactose, glucose, mannose and fructose were the neutral sugars presented in CPS of G. gelatinosa. Acidic sugars including galacturonic and glucuronic acids were also found in CPS. The amount and composition of G. gelatinosa's CPS varied according to its growth phase and culture conditions. The highest amount of acidic sugars was produced when cultured under low light intensity. The extracted CPS rapidly removed Pb2+ from the solution (82.22+/-4.82 mg Pb2+ per g CPS), directly demonstrating its roles in binding Pb2+ ions. Its ability to remove Pb2+ rapidly and efficiently, to grow under sub-optimal conditions (such as low pH and low light intensity), and to produce high amount of CPS with acidic sugars, leads us to conclude that G. gelatinosa is a potential viable bioadsorber for mildly acidic water contaminated with Pb2+.