Itaconic acid (IA) has potential as a compatibilizing agent in polymeric blends due to its unique chemical characteristics. Sodium hypophosphite (SHP) has been studied as a catalyst in esterifying reactions using multicarboxylic acids. Starch/poly(butylene adipate‐co‐terephthalate) blown films containing IA, with and without SHP, were produced. The film containing IA presented higher tensile strength (8.166 MPa) and elongation (891.473%) than the control film (5.548 MPa and 487.637%, respectively). When SHP was added (sample IA‐SHP), tensile strength increased even more (9.215 MPa); however, elongation (636.821%) was lower than in the IA film. This behavior was attributed to crosslinking between two starch itaconoate molecules intermediated by SHP. The increase in the compatibility between the polymeric phases justified the lower permeability to water vapor of the IA‐SHP films and was responsible for the production of films with a more compact and homogeneous structure. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 46629.