In this study, chemically functionalized reinforcements, such as Kenaf fiber (KF) and multi-walled carbon nanotubes (MWCNTs), are used to enhance the crystallinity, mechanical properties and heat resistance of polylactic acid (PLA) composites. The functionalized KF and MWCNTs evidence excellent compatibility in the PLA matrix through the generation of chemical bonding, and a transcrystalline structure is generated around the reinforcements, thereby significantly improving the physical properties. The DSC analysis reveals that functionalized KF can speed up crystalline growth and increase the crystalline content. The annealing treatment further drives the PLA re-crystalization and enhances crystallinity, according to the DSC results. Moreover, the Avrami equation shows that the functionalized KF and MWCNTs are helpful in turning the PLA crystallinity from a 3-dimensional bulk (or sphere) structure into a 2-dimensional sheet structure. (C) 2017 Elsevier B.V. All rights reserved.