The composite materials of biodegradable polymer, poly(lactic acid) (PLA) and fatty acid modified eggshell 15 phr were prepared using a twin screw extruder. Eggshell was modified with different types of fatty acids i.e. propionic acid and oleic acid. Samples were shaped by an injection molding machine to prepare the specimens for mechanical testing. A scanning electron microscope was used to characterize the fracture surface of the composites to ascertain their morphological properties. A universal testing machine and an impact tester were used to investigate the mechanical properties. From the investigation, it was found that the dispersion of eggshell modified with fatty acid in PLA matrix is more uniform than unmodified eggshell. Young’s modulus and tensile strength of the composites between PLA and eggshell modified with propionic acid are higher than neat PLA and PLA/eggshell modified with oleic acid. On the other hands, the relative amount of elongation at break and impact strength of PLA/eggshell modified with propionic acid composite are lower than the composites of PLA and eggshell modified with oleic acid.