The first aim of this study was to compare influences of various contents of the micro- (200 nm) and nano (50 nm)-sized titania (TiO2) particles especially on the mechanical performance of the polylactide (PLA) biopolymer. Micro- and nano-composites were prepared by twin-screw extruder melt mixing, while the specimens were shaped by compression molding. Scanning electron microscope analyses and mechanical tests revealed that due to the most efficient uniform distribution in the matrix, the best improvements in the strength, elastic modulus, and fracture toughness values could be obtained either by using 5 wt% micro-TiO2 or by only 2 wt% nano-TiO2 particles. The second purpose of this study was to investigate influences of using maleic anhydride (MA)-grafted copolymer (PLA-g-MA) compatibilization on the performance of one nanocomposite composition. Due to the improved chemical interfacial adhesion, use of PLA-g-MA compatibilization for the specimen of PLA/2 wt% n-TiO2 composition resulted in the highest improvements in the mechanical performance of neat PLA. The improvements were 14% in tensile strength, 20% in flexural modulus, and as much as 67% in fracture toughness. Thermal behavior of all specimens was also observed by differential scanning calorimetry and thermogravimetric analyses.