Poly(lactic acid) (PLA) loaded with various levels of chitosan nanoparticles (CsNP) (0-5.0%) were prepared by twin-screw extrusion. The nanocomposites were investigated based on their morphology, thermal, mechanical and dielectric properties. The SEM morphology showed that CsNP was dispersed uniformly in the PLA matrix. Thermal analysis through DSC revealed that the cold crystallization temperature of PLA in the case of nanocomposites slightly decreased with increasing content of CsNP; indicating a limit nucleating effect of CsNP. TGA analysis revealed that the incorporation CsNP slightly decreased the thermal stability of the PLA matrix. The mechanical analysis indicated that the incorporation of the CsNP in the PLA matrix improved the elongation and the impact strength, but decreased the tensile strength. The dielectric properties of these materials have been investigated for the a-relaxation process as a function of the temperature and frequency. The a-relaxation process was analyzed with Vogel-Fulcher-Tamman and Havriliak-Negami models and fitting parameters and their evolution were obtained. (C) 2016 Society of Plastics Engineers