Blend films composed of hydroxypropyl cellulose (HPC) and polyethyleneimine (PEI) were prepared by solution casting method. The structure and mechanical properties of the blend films were analyzed by attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy and tensile strength tests. The ATR-FTIR results indicated that there is a 5 cm(-1) band shift to higher wave number due to the formation of hydrogen bonding between HPC and PEI components. The mechanical properties of the blends, such as breaking stress, elongation at break, and Young modulus were greatly affected with increase of PEI component. The contact angles of water, ethylene glycol, formamide, and diiodomethane drops were measured on the blend films. The contact-angle results were evaluated in terms of surface free energy components using van Oss-Good methodology. It was shown that the surface free energy components of HPC and its blends did not differ so much With the composition. However, the apolar Lifshitz-van der Waals component (gamma(LW)(S)) values are higher than those of the Lewis acid-base interactions component (gamma(AB)(S)) values. (C) 2009 Wiley Periodicals, Inc. J Appl Polym Sci 114: 2751-2754, 2009