The objective of this study was to prepare biodegradable chitosan nanocomposite films contained dispersed nanoparticles of methoxy poly(ethylene glycol)-b-poly(ε-caprolactone) (MPEG-b-PCL) or methoxy poly(ethylene glycol)-b-poly(D, L-lactide) (MPEG-b-PDLL) diblock copolymers by solvent evaporation of nanoparticle suspension-chitosan solution. The nanoparticles were firstly produced in the chitosan solution by modified-spontaneous emulsification solvent diffusion method without any surfactants before film casting. The dispersed nanoparticles with approximately 100 and 300 nm in sizes for MPEG-b-PDLL and MPEG-b-PCL, respectively can be observed throughout the chitosan film matrices. Nanoparticle morphology was spherical shapes with smooth surfaces. The nanoparticles of MPEG-b-PDLL were smaller than the MPEG-b-PCL. The possible interactions between the chitosan film matrices and the nanoparticles were evaluated by thermogravimetry. Thermal stability of the chitosan film matrices were enhanced by nanoparticle incorporating. The chitosan/MPEG-b-PCL nanocomposite films had lower film transparency and moisture uptakes than the chitosan/MPEG-b-PDLL nanocomposite films. The both film transparency and moisture uptakes decreased as the diblock copolymer ratio increased. © 2009 Asian Network for Scientific Information.