The aggregate structure of a zinc-neutralized ionomer made from an ethylene-methacrylic acid copolymer was studied as a function of temperature using extended X-ray absorption fine structure (EXAFS) spectroscopy. No gross changes in structure were found in the range 6-450 K, indicating that the aggregate structure remains basically unperturbed over this temperature range under quiescent (no-stress) conditions. Changes in EXAFS spectra were assigned to changes in mean-squared displacement with temperature as expected. At a temperature that corresponds roughly to the melting point of polyethylene, an extremely slight change in EXAFS spectra occurred which might be evidence of minor changes in average aggregate size. No evidence was found for any dramatic changes in structure such as an order-disorder transition or acid salt formation.