Bio-reinforced green composites from biodegradable polymers and natural fibres have received increasing scientific and industrial attention in the fields of packaging, medical and automotive sectors. Poly(lactic acid) (PLA) is one of the most promising biodegradable thermoplastic polyesters with good mechanical properties. However, the insufficient impact strength, inherent brittleness and low thermal stability of PLA limit the scope of its applications. Considerable efforts have been made to improve its properties in order to achieve compatibility with thermoplastics processing and manufacturing, and compete with commodity polymers. Cellulose nanofibrils with lateral dimensions three orders of magnitude smaller than the intact plant fibre cells are an ideal reinforcing material for nanocomposites due to high aspect ratio, large specific surface area and high mechanical strength/weight performance. In this chapter, we review the preparation, structure and properties of PLA/nanocellulose biocomposites with particular focus on the effect of surface modification on nanocellulose dispersion, and the effect of nanocellulose incorporation on crystallization kinetics of PLA matrix and mechanical, thermal and barrier properties of biocomposites.