Co-rotating twin screw extruders are extensively used in polymer compounding. In co-rotating twin screw extruders, the kneading disk region is the most influential for compounding efficiency. However, only a few studies have so far been made for the flow analysis of the kneading disk region. This may be due to the fact that phenomena relating to kneading are overly complicated. In this study, the flow in the kneading disk region was investigated using a closed-type co-rotating twin screw single-staged mixer. We measured torque, pressure, and resin temperature under various compounding conditions of polypropylene. It was found that the flow characteristics obtained were identical with those measured using a capillary rehometer.