This research investigated the impact of different processing temperature (extrusion at 160 degrees C and 180 degrees C) and the influence of the TiO2 and CaCO3 fillers on morphology, mechanical, and thermal properties of polylactide (PLA) blended with low-density polyethylene (PE-LD) and high-density polyethylene (PE-HD) in 90/10 weight ratio. The impact of the particle size of the filler was also examined with the three types of TiO2 filler. It has been shown that the different processing temperature has no significant impact on the morphology, mechanical, and thermal properties of PLA/PE-LD 90/10 and PLA/PE-HD 90/10 polymer blends. It has also been shown that better phase interaction is not the crucial factor for the improvement of the mechanical properties but the domain size distribution of the dispersed phase within the matrix and the dispersion of the filler are. Samples with a narrow size distribution of the dispersed phase domain (5 to 10 mu m) with the higher portion of larger domains that are uniformly distributed within the polymer matrix showed best mechanical properties. POLYM. ENG. SCI., 59:1395-1408 2019. (c) 2019 Society of Plastics Engineers