Abstract: An improved process is provided for the production of stabilized acrylic fibers and films. Certain stabilization promoting agents are incorporated in a solution of an acrylic polymer prior to extruding the same to form a fibrous material or film wherein the pendant nitrile groups present in the acrylic polymer are substantially uncyclized, and the acrylic fibrous material or film having a minor quantity of the stabilization promoting agent incorporated therein is heated in an oxygen-containing atmosphere until a stabilized fibrous material or film is formed which is capable of undergoing carbonization. The stabilization promoting agents employed in the present process are mineral acids, sulfonic acids, certain carboxylic acids, and Lewis acids. The resulting stabilized fibrous material or film is non-burning, and may be utilized as a fire resistant fiber, fabric, or film, or optionally carbonized or carbonized and graphitized to form a carbonaceous fibrous material or film.