The results of investigation of the influence of temperature on the micromechanics of fracture ofpofymethyl methacrylate and epoxy materials in dynamic loading are presented, A method was developed for determination of the value characterizing the formation and development of microcracks in front of the front of the main crack. Anomalous temperature relationships of crack length and the density of microfractures in polymethyl methacrylate were established. The influence of the processes of stress concentration, local inelastic deformation, and thermofluctuation rupture of polymer chains on the micromechanics of fracture of polymers is considered. It is shown that a change in temperature may lead to a qualitative change in the processes of microfractures. The formation of microcracks in front of the front of a propagating crack may transform into outstripping of it by the leading microcracks and the reverse. It is established that a thermofluctuation character is characteristic of fracture of polymers in intense short-term loading.