Poly(lactic acid) (PLA) is a potential green alternative for conventional petroleum-based plastics. However, the brittleness limits its application (e.g., agricultural films, garbage bags, plastic bags, food containers, food packaging). In this study, silane-compatibilized (triethoxyvinylsilane, A-151) bamboo cellulose nanowhiskers (BCNW) were introduced into a PLA matrix to toughen the composites. The A-151 successfully grafted on the surface of cellulose, and the thermal degradation stability of BCNW decreased after A-151 modification. Morphological, tensile and thermal properties of the toughened PLA bionanocomposites were investigated, and the toughen mechanism was clarified. The silane linked BCNW and PLA via Si-O-C bonds and hydrogen bonds. Elongation at break of the composites remarkably increased from 12.3 +/- 1.7% (untreated) to 213.8 +/- 21.6% (16 wt% A-151 treated). Both tensile strength and modulus decreased with the silane treatment. Typical toughness fracture characteristic (wire-drawing) was observed on the fractural surface. Glass transition temperature and crystallinity decreased from 45.6 A degrees C/30.33% (untreated) to 33.6 A degrees C/13.23% (16 wt% A-151 treated).