Since mechanical behaviors of polymeric materials are viscoelastic under load a certain part of energy given from external input force and/or displacement is consumed as loss energy in the material. The consumed loss energy could be changed into thermal energy which leads to heat generation and temperature rise. It is important to evaluate the correlation between temperature change and the amount of loss energy accumulated by mechanical loading. In this study, the authors discuss on temperature rise and its distribution in a soft epoxy resin due to periodic tensile load at several temperatures and make an approach to the evaluation of stress accompanied with heat generation. Firstly, mechanical properties of a soft epoxy resin were measured by dynamic test. Secondly, taking heat generation and temperature rise into account, deformation behavior in rubbery elastic condition is compared with that in viscoelastic one using data obtained by digital image correlation. As the results, remarkable difference of dynamic deformation behaviors under viscoelastic and rubbery conditions was confirmed. Under viscoelastic condition, spatially nonuniform heat generation and conduction lead to nonuniform temperature distribution in the center part of the specimen.