This paper focuses on the use of styrene butadiene rubber (SBR) as a viscosity modifier in novel blends of natural rubber (NR) and dichlorocarbene modified styrene butadiene rubber (DCSBR). The processing characteristics, vulcanisation kinetics, stress-strain behaviour, mechanical properties and low temperature transition of the blends have been examined in order to analyse the influence of SBR in the blends. The change in cross-link density values from stress strain behaviour and equilibrium swelling data has been correlated with the technological properties of the blends. The excellent mechanical properties and the increased cross-link density in blends in the presence of 5-10 phr of styrene butadiene rubber reveals the viscosity modifying action of SBR in NR/DCSBR blends. The variation in viscosities of these blends with the addition of SBR is reflected in the DSC thermograms. The resulting blends show very high resistance to thermal ageing as compared to those without SBR.