The topic of this graduation thesis is the “influence of injection molding parameters on the tensile properties of a polyethylene molded article,” so it was extremely necessary to describe polyethylene and its physical and mechanical characteristics within the thesis, as well as the injection molding process, with a special emphasis on the adjustable injection molding parameters. The first part of the thesis is briefly based on a description of polymers, providing for an insight into that material group, whereas a further emphasis is placed on polyethylene (PE) and its characteristics, as well as on an injection molding procedure and its adjustable parameters. The theoretically analyzed polyethylene, injection molding, and adjustable parameters characteristics are an introduction to the final part of the thesis, in which their influence is experimentally proven. Examined were the melt temperature and the holding pressure, for it was hypothesized that these two parameters exert a significant influence on the polyethylene (PE) tensile properties. The testing took place at the Faculty of Mechanical Engineering in Slavonski Brod. The material used in the molding procedure was the semicrystalline thermoplastic polyethylene PE MG9621B manufactured by Borealis, whereas the equipment applied during the work was the BOY XS injection molding machine, the Regloplas 90s temperature control unit, and the 10-kilonewton Shimadzu AGS-X tensile testing machine. In the thesis, all the obtained measurement data are depicted as tables, diagrams, or histograms.