Blends of two polyethylenes and an elastomer were prepared to investigate the effect of the latter polymer. The blends contain equal parts of low density (LDPE) and linear low density polyethylene (LLDPE), and ethylene-propylene-diene rubber (EPDM) with variable content ranging from 0 to 17.5%. Melt-mixed blends were prepared using a single-screw extruder. The influence on the mechanical properties of the following factors were analysed : EPDM content, stretching rate in the range from 10 to 750 mm/min, and two cooling conditions. From the equilibrium torque the miscibility was analysed. The structure exhibited by the stress-strain (sigma-epsilon) curve of the polyethylenes blend is reduced with the addition of the elastomeric phase, and the ultimate properties increase because the amorphous phase becomes softer and reduces its capability to transmit the applied stress to the crystalline particles. The slope of the sigma-epsilon curve in the strain hardening region shows a maximum value at the stretching rate similar to 50-80 mm/min, which is explained partially in terms of the strain-induced crystallization of the polyethylene components.