The swelling/shrinking behavior of chemically cross-linked poly(vinyl alcohol) (PVA) gel complexed with berate ions in aqueous medium and the intrinsic viscosity behavior of the corresponding polymer solutions were compared as a function of the boric acid concentration, b. The equilibrium swelling ratio of the gels, Q/Q(0), and the intrinsic viscosity ratio of the solutions, [eta]/[eta](0), were in good accordance when the NaOH concentration, [NaOH], is high enough, where Q(0) and [eta](0) are the equilibrium swelling volume of the gel and the intrinsic viscosity of the solution without berate ions, respectively. NaOH was added so as to ionize boric acid. However, a significant difference was observed when [NaOH] was lowered. The comparison of Q/Q(0) and [eta]/[eta](0) allowed one to elucidate the essential difference in the swelling (or expansion) behavior of polymer chains, which is the presence (in a gel) and absence (in a dilute polymer solution) of the Donnan potential. A free energy function for ion-complexed polymer gels is proposed.