The aging of a carboxylated nitrile rubber-epoxy structural film adhesive at 40° C over a period of 15 d has been examined. Properties of the uncured adhesive, the curing reaction, and properties of the cured adhesive have been studied by a number of instrumental techniques. It was found that significant changes occurred in the solubility, epoxy content, and the molecular weight distribution. The cure reaction was “Advanced” but not altered in general form, and the flow during cure was substantially reduced but the mechanical performance of the adhesive was only slightly affected. These results have been interpreted in terms of a carboxyl-epoxy reaction involving the nitrile rubber and epoxy resin.