Aeromonas (A) gum, an acidic heteropolysaccharide, formed aggregates easily in NaCl aqueous solution. A novel solvent of the A gum, which can prevent aggregation, was found to be 0.20M urea/0.25M NaOH aqueous solution. The weight-average molecular weight (M-W), radius of gyration (s(2))(1/2), and intrinsic viscosity ([eta]) of the samples were determined in 0.20M urea/0.25M NaOH aqueous solution at 25 degrees C by light scattering (M-W, (s(2))(1/2)) and viscometry ([eta]). The values of M-W, (S-2)(1/2), and [eta] were close to those in 0.20M lithium chloride/dimethyl-sulfoxide, in which the A gum exists as a semiflexible single chain, implying the same conformation for the A gum in 0.20M urea/0.25M NaOH aqueous solution. The results revealed that 0.20M urea/0.25M NaOH aqueous solution is a good solvent, which effectively avoids the aggregates of the A gum in aqueous solution. Moreover, it can be used to investigate the solution properties and chain conformation of water-insoluble polysaccharides or the polysaccharides that are easily aggregated in aqueous systems. (c) 2005 Wiley Periodicals, Inc.