DSC and TGA studies have been carried out to assess the thermal stability of locally produced polyethylenes with glass fillers. Low and high density polyethylenes (melt flow indices, 20 and 0.35 g per 10 min, respectively) are used with glass powder (GP) or short glass fibers (GF). The filling ratio of glass was varied up to 25% in weight. DSC data showed no remarkable changes in melting point on testing LDPE-glass-filler systems, while a slight reduction in melting point was noticed on measuring different HDPE-GF/GP systems. TGA results indicated a significant improvement in the thermal stability of HDPE-GF/GP systems, while a significant decrease in thermal stability was obtained in the case of LDPE-glass systems.