In this work, poly(lactic acid) (PLA)/graphene oxide nanocomposites were prepared by pre-incorporating noncovalently functionalized GO (f-GO) with didodecyldimethylammonium bromide (DDAB) into PLA via solvent-mixing and subsequently masterbatch-based melt blending. The introduction of only 0.2 wt% f-GO into PLA achieved an extraordinarily 26.6-fold increase in elongation-at-break relative to PLA without sacrificing strengths. Such an extraordinary improvement in toughness was attributed to the excellent exfoliation of GO sheets and appropriate level of interfacial adhesion between PLA and modified GO nanosheets, thus facilitating the yielding of the matrix.