An investigation of the influence of branch length and crystallinity on environmental stress cracking properties of short-chain branch polyethylenes (SBPEs) in Igepal solution is reported. The precise value of Igepal transition time (ITT) and difference between the failure process of SBPEs in air and in Igepal solution were determined by comparing their plots of notch opening displacements vs. time in air and in Igepal solution. Igepal transition time can only be found as the failure time (t(fl)) is greater than the critical time Igepal required to "accelerate" the fracture of SBPEs in Igepal solution. Prior to ITT, time dependence of notch opening displacements and fracture surfaces of samples in Igepal solution were similar to those in air. In contrast, obvious voids appeared in the base of craze and crazelike structures containing clear voids were found on the fracture remnants of samples with tn longer than their ITTs. The value of ITT and t(fl) were found to increase significantly for samples associated with higher crystallinity. However, no significant difference in Value of ITT was found for samples with the same crystallinity, tie-molecule density, molecular weight, branch frequency, but different branch length. Finally, environmental stress cracking resistance (ESCR) and t(fl) of SBPEs in Igepal solution increased dramatically as the short-chain branch length increased. This dramatic improvement in environmental stress cracking properties with short-chain branch length is attributed to the increasing sliding resistance of the polymer chains through the crystal and through the entanglement in amorphous region at time before and after ITT.