Pultrusion is a continuous method for producing profiles with a constant cross section. Because mechanical properties of pultruded composite are related to process parameters, developing a method for flow visualization is essential. In this study pultrusion of thermoplastic polymers was visualized and useful data about polymer flow and void formation during process was obtained. In this regard a straight (converging-parallel) pultrusion die with glass walls has been used for direct observation of process during pultrusion. Glass die has been heated using IR radiation for continuous heat supply and providing enough space to install visualization equipment. Also colored pellets and fibers were used for better visualization. Average velocity of a specific particle was measured in axial and lateral directions Vx=0.43cm/s and Vy=0.05cm/s. The average axial velocity in the entrance part of the die was measured twenty percent lower than puller speed and it gradually converged to puller speed at the end of the die. Volume of voids among the die has been reduced about 0.17 compared with first voids volume in die entrance. By using darcy law, average velocity and 7 bar measured pressure inside die, the axial permeability was calculated 5*10e-8 m2.