Rubber reinforcement increases if the domain size becomes less than 1 mum. Compositions of natural rubber and cellulose II were prepared by co-coagulation of natural latex and cellulose xanthate mixtures. The influence of increasing amount of Cel II, varying from 0 to 30 phr, on processing, curing and mechanical properties were studied. The use of cellulose as filler is related in particular to its crystallinity. The composition with 15 phr of Cel II was found to give the best properties.