Large deformation behavior of two polyolefins has been investigated under high temperatures and high strain rate conditions. During uniaxial tensile tests at constant true strain rate, volume, stress, and deformation ratio were measured. At the temperatures considered, the mechanical behavior tends to be elastic (rate-independent) as strain rate increases. Thus elastic models can be used to describe the deformational behavior of these resins under such conditions. Models proposed by Ogden, by Coleman as modified by Radi, and by Sweeney-Ward have been considered to fit experimental data and their adequacy has been discussed. Sweeney-Ward's model has been found to provide the best fit of the examined polymer's behavior at high temperatures and high strain rates.