The results of investigation of nonlinear viscoelastic properties of filled elastomer on the base of nitril-butadiene rubber filled by nanoparticles of technical carbon N-110 are presented. The tests of material on the stress relaxation under tension were carried out in wide range of deformations at two values of temperature – 20 oC and 50 oC. On the base of obtained experimental data it was shown that the relaxation modulus of the investigated material (the ratio of current value of stress to given value of strain) dependences essentially on strain. The inherited type nonlinear constitutive equations were taken to description of obtained experimental data. These equations suppose the introduction of added functions to take into account of the influence of strain on the viscoelastic properties of material. The use of this approach enables us to represent of the experimental relaxation curves at different values of strain in the form of generalized dependencies of the reduced relaxation modulus on time. These dependencies were used to identification of characteristics of viscoelastic behavior of material. The influence of temperature on the viscoelastic properties of material was taken into account on the base of the time-temperature analogy method.