In this paper, cellulose nanoparticles (CN) were coagulated from a NaOH/urea/H 2O solution of microcrystalline cellulose (MC) using an ethanol/HCl aqueous solution as the precipitant. CN ranged in size from about 50 to 100 nm. Compared to MC, CN formed a new crystalline lattice of cellulose II. The glycerol plasticized-wheat starch (GPS)/CN nanocomposites were prepared using CN as filler in GPS matrix by a casting process. At a low loading level, CN was dispersed evenly in the GPS matrix. The tensile strength increased from 3.15 to 10.98 MPa when CN content went from 0 to 5 wt.%. CN may increase the thermal stability of GPS/CN composites. Moreover, water vapor permeability decreased from 5.75 × 10 −10 to 3.43 × 10 −10 g m −1 s −1 Pa −1. The improvements in these properties may be attributed to the good interaction between CN filler and GPS matrix because of the similar polysaccharide structures of cellulose and starch.