Abstract In this research, the combinations of silica (SiO 2 ), with either graphite (GR) or graphene oxide (GO), are studied as hybrid reinforcements of natural rubber (NR). Whereas individual improvements of rigidity, strength or ductility can be obtained depending on the composition, a synergistic reinforcement is specifically evidenced after addition of GO/SiO 2 with a 3:1 ratio. For this formulation, both strength and modulus drastically increase while keeping the strain at break at a decent level. From the confrontation of all tensile tests results with theoretical reinforcement models, a good correlation between the experimental data and the Guth Gold model is observed, which reveals that the mechanical properties should essentially be governed by the filler/matrix interactions. This assumption has been discussed through the cooperative rearranging region (CRR) concept, by analyzing the calorimetric response of the nanocomposites at the glass transition. Not only the 3:1 GO/SiO 2 composition is the only one for which the glass transition clearly shifts to higher temperatures, its CRR average size is also the lowest in comparison with reference NR. This result, interpreted as the signature of the most efficient intercalation of the fillers, matches well with the steep strain hardening recorded for this nanocomposite.