By utilizing the interaction of alpha-cyclodextrin (alpha-CD) with dodecyl side chains in polymers of x mol-% dodecyl-modified poly(acrylic acid) (p(AA/C-12(x))), systems that undergo sol-to-gel transitions were successfully constructed. Rheological experiments indicated that addition of alpha-CD to the hydrogel of p(AA/C-12(5)) caused a drastic decrease in the viscosity, while addition of oligo(alpha-CD) to the solution of p(AA/C-12(2)) led to a remarkable increase in the viscosity.