Abstract. The experimental study deals with the effect of modification of the surface layer by irradiation cross-linking on the micromechanical properties of the low-density polyethylene (LDPE) tested using the instrumented nanohardness test. The surface layer of LDPE specimen made by injection technology was modified by irradiation cross-linking using beta irradiation, which significantly influences micromechanical properties of the surface layer. Compared to the heat and chemical-heat treatment of metal materials (e.g. hardening, nitridation, case hardening), crosslinking in polymers affects the surfaces in micro layers. These micromechanical changes of the surface layer are observed in the instrumented microhardness test. Our research confirms the comparable properties of surface layer of irradiated LDPE with highly efficient polymers. The subject of this research is the influence of irradiation dosage on the changes of micromechanical properties of surface layer of LDPE.Introduction. Low-density polyethylene (LDPE) is a commodity polymer used extensively in extrusion operations such as coating, blown film, blow molding, and foaming. Extrusion of LDPE foams by direct gas injection or the so-called physical foaming can be separated in to five distinctive steps, i.e. melting of the solid LDPE pellets, injection and mixing of the liquid gas in the molten LDPE, cooling and shaping of the melt into the expansion condition, foaming of the melt by the expanding gas and finally cooling of the foam. Although viscosity and melting/crystallization behavior plays an important role in each or most of these process steps, the gas expansion is the crucial step in the foam process. In order to obtain a good foam quality (regular fine cell size and high closed cell content), the gas laden melt needs to be cooled down to a temperature close to the crystallization temperature of the semi-crystalline polyolefin to increase the melt viscosity and reduce the time needed for the transition from melt to solid phase. In practice, this means for semicrystalline LDPE that the temperature of the melt at the die exit is always a few degree centigrade above the crystallization temperature [1][2][3][4].