We have encapsulated the polyoxoanions [P₂W₁₈O₆₂]⁶⁻ and [P₂W₁₅V₃O₆₂]⁹⁻ in a self-assembled carboxy-methyl-chitosan (CMC) hydrogel, exhibiting a regular superstructure in water at physiological pH. We performed stability studies as a function of temperature and polyoxometalate (POM) loading, and observed exceptional T_gel properties. This work is a step forward towards developing biologically active polyoxometalate-based materials.