Composites of natural rubber (NR) and cellulose II ( Cel II) were prepared by co-coagulation of natural latex and cellulose xanthate mixtures. The influence of increasing amounts of Cel II, varying from 0 to 30 phr, on the mechanical properties was investigated. The topography of the fracture surfaces of tensile, tear and abrasion specimens after testing was observed by scanning electron microscopy (SEM). The fracture surface morphology was correlated with the mechanical properties. As the cellulose II content increases, the materials showed a gradual change in the mechanical properties and in the fracture mechanisms. The composite with 15 phr of Cel II was found to give the best tensile and tear performances. The failure surfaces and the fracture mechanisms of unfilled and filled natural rubber composites depended on the nature of the test-tensile, tear or abrasion. The SEM evaluation of the tensile fracture surfaces was the best observation method to show the effect of cellulose II on the elastomeric matrix. (C) 2003 Kluwer Academic Publishers.