Carbon nanotubes (CNTs) reinforced natural rubber (NR) composites with the CNT contents of 1, 3, 5, 10 and 20 wt% were synthesized using a solution casting method. The morphology of the composites was observed by scanning electron microscopy and Fourier transform infrared spectroscopy. It was found that CNTs were well distributed into NR and there was an excellent interface between CNTs and natural rubber. The mechanical properties of the composites were investigated by dynamic mechanical analysis (DMA) test and tensile test. It was found that the increment of storage modulus of NR/CNT composites was about 0.42 MPa/wt% in the rubbery state which agreed well with the results of tensile test. The large modulus increment confirmed the reinforcement effect of carbon nanotubes.