The aggregation and disaggregation of Aeromonas (A) gum, an acidic heteropolysaccharide, were investigated by viscometry, a fluorescent probe, and gel permeation chromatography combined with laser light scattering techniques in aqueous solutions containing desired NaCl at different temperatures. The A gum had a strong tendency of aggregation and high viscosity in the aqueous solutions. The weight-average molecular weight, z-average radius of gyration, weight-average molar number (omega(ag)), and apparent aggregation number (N-ap) of the aggregates were investigated and discussed. The results indicated that there were three regions that corresponded to three kinds of aggregates and two transition temperatures at about 35 and 75 degrees C in the disaggregation course. When the temperature was higher than 75 degrees C, the omega(ag) hardly changed, and there was still a certain amount of aggregates even at 100 degrees C, indicating that the aggregates were difficult to disrupt completely. Moreover, the aggregation was thermally irreversible. Decreasing polysaccharide concentration reduced the content of the aggregate. However, N-ap remained constant around 20, independent of the polysaccharide concentration in a 0.5 M NaCl aqueous solution at 25 degrees C. At a salt concentration greater than or equal to 0.05 M, the aggregation was almost independent of the salt concentration used here.