We have studied on the conditions to make uniform microvoids inside a film by blending with polyethyleneterephthalate, polypropylene and titanium dioxide in order to produce microvoided films with light weight like paper, high whiteness and brilliant mechanical properties. In twin screw extruder with length to diameter ratio(L/D), 40, it was possible to get the highest tensile strength at specific throughput of 0.05 kg/h with the extrusion amount of 20 kg/h and screw rotational speed of 400 rpm, and to satisfy the good mechanical properties and low density at the blending conditions of polyethyleneterephthalate, 88 wt% and polypropylene, 12 wt%. It was found that the dispersion property of titanium dioxide affected the density and mechanical properties of microvoided films and the effect was best at the condition of 15 mgPO₄^-3/g as the surfactant on titanium dioxide surfaces.