In the paper, a characterization of autothermal and conventional extrusion processes of low＇ density polyethylene (LDPE) in the typical single screw extruder equipped with a classical screw was presented. It was shown that autothermal (adiabatic) extrusion process is characterized by better effectivity factors than a conventional extrusion process carried out in the same basic extrusion conditions. In both processes the mass flow rate, total extruder power, total energy consumption per unit mass, extruder energy efficiency, extrusion velocity, temperature distribution along the plasticating system and extruder head,were compared. The attempt to present shear stress and flow rate distribution during laminar and isothermal flow of the non-Newtonian fluid through the circular channel (extrusion die) was undertaken, Appropriate dependences of experimental factors on the rotational speed and angular frequency of the screw were made. Appropriate conclusions were drawn.