New applications of both pea hull fiber (PHF) and PHF-derived nanowhiskers (PHFNW), isolated from PHF by acid-hydrolysis, as fillers in starch-based biocomposite films were explored in this work. Two series of films were prepared by blending pea starch (PS), respectively, with PHF and PHFNW. The effects of PHF and PHFNW as filler on the structure and properties of the composite films were comparatively investigated by observation of morphology and analysis of thermal, optical, and mechanical properties. The results revealed that the PS/PHFNW nanocomposite films exhibited improved physical properties over both the neat PS film and PS/PHF microcomposite films. The light transmittance at 800 nm, tensile strength, elongation at break, and Young's modulus were 56.0%, 4.1 MPa (Megapascal), 30.1%, 40.3 MPa, respectively, for the PS film without filler; 58.0%, 7.6 MPa, 41.8%, and 415.2 MPa for the PS/PHFNW film containing 10 wt% filler; and 37.2%, 2.8 MPa, 17.0%, and 29.8 MPa for the PS/PHF film containing 10 wt% filler. The improvement to the properties of PS/PHFNW nanocomposite films may be attributed to the nanometer size effect of PHFNW, which resulted in the homogeneous dispersion of PHFNW within the PS, and the strong interactions between the matrix and the nanoscale filler. POLYM. ENG. SCI., 49:369-378, 2009. Published by the Society of Plastics Engineers