The effect of gamma irradiation, in acetylene, on large diameter oriented polyethylene has been investigated. The dependency of gel content, melting point, and crystallinity on dose was evaluated. The gel content dose relationship showed two regions, indicating that an effective network is formed at low doses, 60 kGy. Irradiating the oriented rod in acetylene was found to more than double the initial tensile modulus. This improvement in the tensile properties resulted in improved creep–strain resistance for the material. These improvements in the mechanical properties were attributed to crosslinks formed both in the amorphous regions and at the surfaces of the crystalline regions. At high does > 180 kGy degradation of the oriented polymer resulted in a deterioration in mechanical properties.