The thermoplastic elastomers have been widely used in polymer blends to improve their mechanical properties. This work is about the study of chemical modification of styrene-butadiene-styrene (SBS) with maleic anhydride (MA) by radical reaction. The functionalization reaction was carried out in a mixer Haake Rheomix 600 and the torque variation was monitored during the process. The products were characterized by Infrared Spectroscopy (FTIR) and crosslinking was evaluated by extraction. A calibration curve was plotted to determine the functionality. The results showed that it is possible to accomplish the functionalization reaction avoiding the crosslinking.