The strength properties of natural rubber vulcanizates, which are widely used in automobile engine mounts and bushes, are important to evaluate the lives of the automobile rubber parts that can withstand together with those of automobile. The tearing energy and flex fatigue life were investigated, with three diffrent types of vulcanizing system (i.e. ‘conventional’, ‘efficient’, and ‘peroxide’ vulcanizing system) in both ‘initial’ and ‘aged’ state. Each stock was made based on same Rheometer torque difference between Tmax and Tmin. Tearing energies were investigated by ‘trouser’ test method using fabric reinforced test pieces over nine different rates of crack propagation. Flex fatigue life was also examined by means of De Mattia flex test. They show that polysulphide type crosslinking, which is commonly known as the most fatigue resistant natural rubber vulcanizate, was not essential to get a high flex fatigue resistance.