Blends of elastomeric chlorinated polyethylene (CPE) and natural rubber (NR) at blend composition ratio of 80/20 CPE/NR with various precipitated silica loadings were prepared. By the use of rheological approaches, a mechanism of silica reinforcement was proposed. Results obtained reveal that the viscoelastic behavior of blends is influenced remarkably by loadings of silica. A cure promotion phenomenon is found as silica is loaded due probably to the strong silica-CPE interaction and/or a reduction in curative absorption on silica surfaces. A strong Payne effect is observed, which is increased by a rise in silica loading, implying a formation of pseudocros-slink via a physical interaction, which could be disrupted at high strain of deformation. The proposed mechanism of silica reinforcement based on the formation of pseudocros-slink is validated by the deactivation of silanol groups on silica surfaces using silane-coupling agents. The bis-(3-triethoxysilylpropyl) tetrasulfane (Si-69) is found to be more effective in suppressing the pseudocrosslink than 3-thiocyanatopropyl triethoxy silane (Si-264), which is thought to be the result of its larger amount of alkoxy groups at a given silane loading. (c) 2007 Wiley Periodicals, Inc.