Abstract: An improved process is provided whereby acrylic fibers are thermally stabilized (i.e., rendered black in appearance and non-burning when subjected to an ordinary match flame). The acrylic fibrous material, while present in an oxygen-containing atmosphere, is subjected to the intermittent irradiation of a laser beam which surprisingly has been found to expedite the desired thermal stabilization when compared to commonly employed processes which transfer heat to the acrylic fibers primarily by the convective flow of a heated gas (e.g., air) while the acrylic fibers are suspended in a hot gas oven. In a preferred embodiment the laser beam is produced by the use of a CO.sub.2 infrared laser.