AbstractFracture mechanics was used to investigate the environmental stress cracking of low‐density polyethylene with 4.0 melt flow index. Annealed samples were prepared; a single edge notch was made and then the samples were fractured under constant load in four different liquid alcohols. The relation between the stress intensity factorKand the crack speeda˙has been investigated. The loga˙vs. logKcurves are influenced not only by temperature but also by the alcohol used as the environment. This influence has been studied in detail. The conclusions are as follows: the crack speed at highKis determined by the diffusion mechanism, and this mechanism cannot be explained in terms of hydrodynamics but can be explained in terms of thermally activated molecular motion. On the other hand, the crack speed at lowKis strongly related to the plasticization and the stress relaxation of the crack tip mater