Balanced strength and toughness is always the goal of high-performance polymer materials for practical applications. In this work, a series of transparent poly(lactic acid) (PLA) nanocomposite films incorporated with fully exfoliated octadecylamine-functionalized graphene (ODAG) as effective nanofiller were prepared by solution blending and casting method. Because of the good hydrophobic compatibility between ODAG and PLA, a homogeneous dispersion of ODAG into PLA matrix and improved interfacial adhesion between them can be achieved. The obtained PLA/ODAG nanocomposite films present markedly improved crystallization behavior, mechanical properties and thermal stability. Compared to neat PLA, the nanocomposite films show a 34% increase in tensile strength, 44% increase in Young's modulus, and 300% improvement in tensile toughness by the addition of only 0.4 wt% of ODAG. The simultaneous improvement in both strength and toughness could be attributed to homogeneous dispersion of ODAG in PLA matrix, improved interfacial interaction due to unique interphase structure, as well as enhanced crystallization. (C) 2014 Elsevier B.V. All rights reserved.