Nanocomposites of nitrile rubber (NBR) and cellulose II (Cel II) were prepared by co-coagulation of nitrile rubber latex and cellulose xanthate mixtures. The effect of the addition of increasing amounts of Cell II, varying from 0 to 30 phr, on the mechanical behavior of a NBR was analyzed. The fracture mechanisms of the nitrile rubber-cellulose II (NBR/Cel II) nanocomposites after tension and tear tests was investigated by scanning electron microscopy (SEM) and correlated to the test results. It was found that the addition of Cell II to NBR leads to a gradual change in the stress at break, and the samples with 20 phr of Cel II showed the highest resistance; as the cellulose content is increased to 30 phr, the strain at break decreases. The SEM fractographic analyses of NBR/Cel II nanocomposites, with cellulose content up to 30 support the observed mechanical behavior of the material. The results are presented and discussed. The obtainment of NBR/Cel II nanocomposites was proven by transmission electron microscopy (TEM).