We report on ferroelectric properties of the monoclinic BiFeO3 thin films grown on (001) and (110) SrTiO3 substrates. Structural analysis using X-ray diffractometer and the electrical characterization of ferroelectricity reveal that the elastic constraint induced by the crystallographic orientation affects the remnant polarization values and retention properties of BiFeO3. The in-depth analysis based on the Williamson-Hall plot and thermodynamic analysis manifests that inhomogeneous strain related to the strain relaxation in the film is responsible for the change of the out-of-plane polarization and retention property of BiFeO3 thin films depending on the substrate orientation. (C) 2016 Elsevier B.V. All rights reserved.