Abstract: SBR/ C₁₈MMT and SBR/ Na-MMT composites were prepared through a melt intercalation process.The result s of XRD and TEM observation show that the dispersion of montmorillonite layers in SBR mat rix is determined by the hydrophobic property of the layers. Organic t reated montmorillonite could be exfoliated into layerswith about 20nm in thickness and uniformly dispersed in the SBR mat rix. The effect s of montmorillonite on the vulcanization reaction of SBR were determined by DSC method. The vulcanization curves show that the existence of C₁₈-MMT accelerates the vulcanization reaction and the activation energy is not changed. For the SBR reinforced by Na-MMT , the vulcanization was impeded and the sensitivity of reaction to temperature was decreased , which resulted inthe decrease of apparent activity energy. Due to the nanoscale dispersion of layers of C₁₈-MMT and the enhancedcrosslinking density of rubber mat rix , the mechanical properties of SBR dramatically increase. The tensile st rengthand 300 % modulus of SBR/ C₁₈-MMT nanocomposite were correspondent to the SBR reinforced by equal content ofcarbon black N330 while the elongation at the break of the nanocomposite was much higher , which is related to theslipping and oriented arranging of the C₁₈-MMT layers in the composite under tension.