Polylactic acid and calcium phosphate composites are widely used in orthopedic fixation applications and are a great alternative to metal materials. However, due to their biological properties and poor mechanical strength compared to metals, they exhibit biocompatibility and acceptable biodegradability properties. In order to make the best of a nanocomposite composed of ceramic nanoparticles, the important issues in this study such as, synthesis of hydroxyapatite nanoparticles and thermoplastic starch microparticles, fabrication and evaluation PLA / HA nanocomposite and its processability, characterizing and evaluating mechanical and structural properties and morphology of nanocomposite, and finally in vitro evaluation of degradability properties in order to simulate the behavior of material degradation within the body were studied. Having examined and analyzing the results of various tests, it was concluded that the use of very small fractions of hydroxyapatite nanoparticles (about 1 or 5 wt.%) ultimate tensile strength improved as an acceptable 11 percent in comparison to the neat polymer. These materials also increased the value of strain to failure (which is a good indicator of toughness in materials) in thermoplastic polyurethane-containing specimens to 15 times higher than the neat PLA. The toughness energy achieved through the area under the stress-strain curve improved by 11 times. The mixed-mode fracture toughness test that is so well recieved for observing the behavior of material in general conditions, showed that the amount of fracture energy improved with the presence of hydroxyapatite nanoparticles by 18 percent. Improvement of mechanical properties continued to 5 wt% of hydroxyapatite nanoparticles, which is considered as the threshold for the reinforcement of the nanocomposite component. At higher wight fractions of HA, the composite strenght decreased due to increased brittleness and aglomeration of nanohyrodroxyapatite nanoparticles. The in vitro degredation test carried out under biological conditions for 28 days indicated that with increasing the weight fraction of hydroxyapatite nanoparticles, the degradation rate in the composite increases and the highest weight loss was observed for starch samples with a 3% of the initial weight. Keywords: Polylactic acid, nanohydroxyapatite, mixed-mode fracture toughness, in vitro degradation