Chitosan/tripolyphosphate nanoparticles were prepared and incorporated in hydroxypropyl methylcellulose (HPMC) films. FT-IR and transmission electron microscopy (TEM) analyses of the nanoparticles. mechanical properties. water vapor permeability, thermal stability, scanning electron microscopy (SEM) of the films were analyzed. Incorporation of chitosan nanoparticles in the films improved their mechanical and film barrier properties significantly. The chitosan nanoparticles tend to occupy the empty spaces in the pores of the HPMC matrix, increasing the collapse of the pores and thereby improving film tensile properties and water vapor permeability. The thermal stability of the films increased with addition of nanoparticles. This study is the first to investigate the use of CS-TPP nanoparticles for the purpose of strengthening HPMC films. (c) 2008 Elsevier Ltd. All rights reserved.