The increasing amount of tires used in the industry induces the researchers to find alternatives to the recycling of the end-of-life tires. Several alternatives in order to application of ground tire rubber GTR include their incorporation as a filler in composites. The main issue in this approach is the lack of compatibility between GTR and polymer matrix. In order to solve this problem the devulcanization by microwaves has been proposed as an interesting approach in order to improve the subsequent crosslinking when the GTR is incorporated to an elastomeric matrix and subsequently co-vulcanizated. In this article a blend formed by natural rubber NR and nitrile butadiene rubber NBR has been proposed as a suitable matrix for composites including GTR. In order to improve the compatibility, the GTR was treated by microwaves prior to its application as semi-reinforcement in rubber matrix. The results indicate that the pretreatment of GTR by microwaves improves the cross-linking and co-vulcanization of used elastomers, what have a positive influence on the mechanical behaviour and microstructure of the NR/NBR/GTR composites evaluated by tensile tests, equilibrium swelling, Thermo Gravimetric Analysis (TGA), Infrared Spectroscopy (FTIR) and Scanning Electronic Microscopy (SEM)