Deformation behavior of several polyethylenes and ethylene-based copolymers with various molecular architecture (linear and branched polyethylene, ethylene based copolymers), and a broad range of molecular mass and its distribution, was studied. Due to the differences in molecular characteristic, this series exhibited a relatively broad range of crystallite sizes as well as crystallinity level, varying from less than 10% up to more than 70%. The samples of polyethylenes and copolymers were subjected to high-strain compression in the plane-strain conditions. The true strain exceeded frequently the value of 2 (a corresponding deformation ratio up to around 10). Plastic deformation to high strain was associated with an intense strain-hardening, leading to very high stress, above 500 MPa. It was found that the yield behavior and the stress of plastic flow depended mainly on the amount of amorphous and crystalline components and on the thickness of lamellar crystals, while the strain hardening behavior depended primarily on the density of chain entanglements in the amorphous component, which in turn was controlled by molecular mass and chain architecture of the polymer, both influencing the process of network modification upon crystallization. (c) 2005 Elsevier Ltd. All rights reserved.