Prevalence of oxidation reactions through electron-beam (EB) treatment of microporous polyethylene membranes under various atmospheres and over a range of doses was investigated to determine the appropriate conditions assisting the viability of crosslinking. EB treatment in air promoted oxidation of membranes so that no gel content was measured, however, this made them slightly less hydrophobic. Although there was a reduction in the oxidation reactions when performing the EB treatment under vacuum, but no detectable gel content was yet found which was assumed to be due to post-irradiation oxidation reactions via trapped radicals upon exposing the EB modified membranes to the air ambient. Therefore, in another experiment designated as VacuumN2, the membrane was kept under nitrogen gas immediately after EB treatment in vacuum allowing the decay of trapped radicals in an inert atmosphere. Consequently, oxidation reactions were practically eliminated leading to a measurable amount of gel content in EB modified membrane under VacuumN2. Additionally, SEM micrographs of EB modified membrane under VacuumN2 verified the enhanced thermal stability by rather preserving the original pattern of the membrane subsequent to thermal annealing close to its melting temperature. Furthermore, regarding the DSC analysis of EB modified membranes, it was overall found that crystallization exotherms are more affected than melting endotherms by the conditions during and after EB treatment.