Nylon cords are extensively used in cord reinforced rubber composites. These cords exhibit complex responses when subjected to actual thermal and mechanical loading conditions. The response is geneally nonlinear and sensitive to time, temperature and moisture content. In this paper, these cords are modeled as nonlinear viscoelastic materials. The cords are treated as one-dimensional structures. This is a reasonable assumption for most practical purposes and furthermore admits more general type of constitutive relations. An experimental program has also been carried out to obtain the viscoelastic properties of these cords as functions of the pre-straining, frequency, and the temperature. The experimental results will be presented and will be compared with the trends suggested by the theoretical developments.