Abstract: In this study, the hybrid effect of nanocellulose/carbon nanotube (NCC/CNT) reinforcement on natural rubber (NR) nanocomposites was investigated. To this end, three series of NR nanocomposites were prepared: NCC/NR, CNT/NR and NCC/CNT/NR. First, the nanocomposites morphology and the filler–rubber interactions were studied using scanning electron microscopy (SEM) and the swelling behavior in toluene, respectively. The results showed that the presence of NCC improved the NCC/CNT hybrid filler dispersion forming a 3D network, while the presence of CNT increased the filler–matrix interaction. The curing results also confirmed that the degree of crosslinking increased when hybrid fillers were used, but the curing time was not modified. In addition, it was observed that using a NCC/CNT hybrid system led to superior mechanical properties, dynamic mechanical properties and thermal conductivity than each material used separately. When 10 phr hybrid filler (with a filler ratio of 1) was added to NR, the tensile strength, modulus at 300% elongation (M300), storage modulus at 10% strain and thermal conductivity were all increased by 57%, 137%, 120%, and 30%, respectively. The results also showed that the NR nanocomposites properties can be controlled by tuning the NCC/CNT filler ratio.