Due to its renewability and biodegradability, biopolymers have developed interest in order to substitute oil-derived plastics. In particular, polylactic acid (PLA) is a promising biopolymer in terms of mechanical and biodegradable properties that is used for different applications. Nevertheless, PLA has some disadvantages like brittleness and processing instability. In order to overcome these drawbacks, it has been blended with natural fibers, leading to a fully biodegradable biocomposite material with enhanced properties. However, blending a hydrophobic biopolymer with hydrophilic fibers leads to poor interfacial adhesion producing interfacial voids, cavities and defects and consequently low performance properties. In this sense, this article reviews different strategies of biopolymer functionalization to improve compatibility in biocomposite materials. First, the effect of different parameters on biopolymers functionalization via melt and reactive extrusion processes is discussed. Finally, coupling efficiency of functionalized biopolymers is analyzed in terms of mechanical and thermal properties.