The acrylic fibers containing 10.8 wt % of acrylic acid as a comonomer were treated with 5% aqueous solution of sulphates of alkali metals (sodium and potassium) and transition metals (cobalt and nickel) at 90 degrees C for 5 min. The effect of this treatment on the chemical structure, thermal behavior and mechanical properties of this fiber was investigated through FTIR, X-ray, DSC, and TGA techniques. The changes in the chemical structure of the fibers have been noticed as a change in the intensity of characteristic infrared absorption bands. Broadening of the absorption band at 1700 cm(-1) due to COO- stretch is also noticed in the case of fibers treated with salts of alkali metals, probably because of formation of a COO-M+ structure. WAXD studies of the fibers treated with metal salts showed the decrease in the crystallinity of the treated fibers. DSC curves of metalated fibers showed the onset of exothermic cyclization at a higher temperature. The initial modulus of the samples increased after this treatment. The fibers treated with sulphates of alkali metals showed an approximately twofold increase in elongation at break compared to the untreated ones.