The non-linear viscoelastic properties of alginate gels were investigated using torsion and compression rheological tests. Like many biopolymers, alginate gels showed strain-hardening behavior during large deformation, and the degree of strain-hardening depended on gel composition. The strain-hardening behavior of alginate gels was attributed to the deformation of rod-like junction zones serving as physical crosslinks in the gel. A constitutive equation based on the deformation of junction zones and a Gaussian distribution network of chains was developed to predict deformation behavior. The resulting equation effectively described the experimental data during torsion and compression, supporting the proposed mechanism that strain-hardening originates from the deformation of alginate junction zones. (c) 2006 Elsevier Ltd. All rights reserved.