The behavior of absorbed water in equilibrium-swollen poly(acrylamide-co-sodium acrylate) [P(Am-NaA)] hydrogel was studied using the pulsed-gradient spin-echo (PGSE) nuclear magnetic resonance (NMR) technique. The observed nonexponential decay of the PGSE signal can be described satisfactorily by a sum of three discrete exponential terms. The self-diffusion coefficient and amount each of three phases' water can be determined quantitatively. By analysis these data, the swelling ratio of hydrogel P(Am-NaA) system in an equilibrium swollen state can be determined.