Studies on rheological and die swell behaviour of natural rubber melts were carried out in aDavenport Capillary Rheometer. Two types of rubber, a Standard Malaysian Rubber (SMR-L) and a viscosity stabilised form of SMR (SMR CV-70) were masticated in a two-roll mill at 50 degree C for different time invervals. The extent of mastication is expressed as plasticity, measured from Wallace rapid plastimeter. Both type of rubbers have shown pseudoplastic behaviour with the value of Non-Newtonian index, n, varying between 0.1675 and 0.2695 under different levels of mastication. Die swell increases with plasticity and shear stress, but decreases with increasing levels of mastication. The value of non-Newtonian index first decreases with plasticity and then increases. The apparent viscosity is found to decrease with the rate of shear and the extent of mastication. It is also established that the power-law model describes the behaviour of both masticated and unmasticated rubber.