The goal of this work was to produce nanocomposites based on poly(lactic acid) (PLA) and cellulose nanowhiskers (CNW). The CNW were treated with either tert-butanol or a surfactant in order to find a system that would show flow birefringence in chloroform. The nanocomposites were prepared by incorporating 5 wt% of the different CNW into a PLA matrix using solution casting. Field emission scanning electron microscopy showed that untreated whiskers formed flakes, while tert-butanol treated whiskers formed loose networks during freeze drying. The surfactant treated whiskers showed flow birefringence in chloroform and transmission electron microscopy showed that these whiskers produced a well dispersed nanocomposite. Thermogravimetric analysis indicated that both whiskers and composite materials were thermally stable in the region between 25 C and 220 C. The dynamic mechanical thermal analysis showed that both the untreated and the tert-butanol treated whiskers were able to improve the storage modulus of PLA at higher temperatures and a 20 C shift in the tand peak was recorded for the tert-butanol treated whiskers.