Genipin, a naturally occurring crosslinker, was employed to modify agarose in aqueous medium at pH similar to 7 at ambient conditions. The physical and rheological properties were studied. The genipin-fixed agarose hydrogel (0.8 wt % genipin with respect to the polysaccharide) having the maximum swelling capacity was obtained after 85-h crosslinking reaction. The reaction mixture developed a dark blue color with the passage of time, indicating thereby the progress of the crosslinking reaction in presence of genipin. The maximum swelling of the genipin-fixed agarose hydrogel in acidic medium at pH 1.2 was similar to 48 g/g, whereas the parent polysaccharide agarose achieved equilibrium swelling state at 6 g/g. The genipin-fixed agarose showed 30% weight loss in Ringer's solution, while the agarose polysaccharide exhibited similar to 50% weight loss in the same medium, both after 60 days. The thermogravimetric analysis studies revealed enhanced thermal stability of the genipin-fixed agarose hydrogel. In view of the enhanced stability and swelling capacity of the genipin-fixed agarose compared to agarose, the value added polysaccharide may be useful in new applications as super absorbents and in biomedical applications. (c) 2007 Wiley Periodicals, Inc.