The rheological behavior of chitosan/alginate solutions was investigated in relation to gelation and polyelectrolyte complex (PEC) formation. Before mixing, the chitosan and the alginate solutions were both homogeneous fluids. However, heterogeneity developed after mixing, accompanied by a serious increase of viscosity. To determine the sol-gel state of the solutions, the viscoelastic variables, such as the dynamic storage modulus (G') and loss modulus (G"), the loss tangent, and the viscoelastic exponents for G' and G", were obtained. Depending on the concentration, the chitosan/alginate solutions revealed unexpected rheological behavior. At a polymer concentration of 1.0 wt %, the chitosan/alginate solution was in a viscoelastic gel state, whereas, at higher concentrations, viscoelastic sol properties were dominant. A viscoelastic gel state for the chitosan/alginate solution was induced based on the weak formation of fiber-shaped precipitates of a PEC at a low polymer concentration. (c) 2007 Wiley Periodicals, Inc.