The work presents the results of experimental studies of selected mechanical properties of plasticized poly(vinyl chloride) extruded by a single-screw extruder with a modified feed section. The variable factors were: feed opening width, feed pocket depth in the extruder barrel and the rotational speed of the screw. The following parameters were studied: yield strength ReH (MPa), tensile strength R-m (MPa), percentage total extension at maximum force epsilon(m) (%), Shore hardness H (degrees ShA). It was found that the increase in the depth of the pocket and the decrease in the width of the feed opening in the studied range increase mechanical properties (besides percentage total extension at maximum force). It was determined that the increase of the screw speed and the simultaneous displacement of both the axis and edge of the feed opening in relation to the plasticizing system axis towards the direction of revolutions of the screw is favorable.