Chitosan may be chemically modified by reductive amination leading to the grafting of hydrophobic alkyl chains along the hydrophilic macromolecular chain. This allows to obtain amphiphilic polymers whose the hydrophobicity (or the hydrophile-lipophile balance, HLB) may be adjusted according to the length of the grafted alkyl chain or the degree of substitution of the amine functions. The existence of hydrophobic interactions between the alkyl chains will change the physico-chemical properties of the solutions of the modified chitosans. These properties are studied and the study is particularly focused on the influence of the polymer concentration and temperature on them and applications as rheology modifiers. Threshold concentrations, over which the polymer solutions have peculiar temperature behaviour, were defined. According to their structure it is possible to prepare solutions with constant viscosity or increasing one with temperature. (C) 2004 Elsevier Ltd. All rights reserved.