BaTiO3/polycarbonate (BT/PC) composite films with different concentration of BaTiO3 ferroelectric nanocrystals are prepared by a spin coating method. The polarization and dielectric relaxation behaviors of BT/PC composite films are characterized by the introduction of orientational order parameter (phi) through in-situ transmission spectrum measurement. It's found that 15% BT/PC composite film has the largest orientation change with the phi value of 10.5% and slow dielectric relaxation, almost 10% decay of phi after 24 h. The optical band-gap of 15% BT/PC composite film decreases after poling indicates that the orientation of BaTiO3 ferroelectric nanocrystals aligns due to the effect of polarization, from 3.8 eV to 3.67 eV. From the XRD results, we consider that the preferential alignment orientation of BaTiO3 ferroelectric nanocrystals after poling is [001]. This suggests that in-situ transmittance measurement is a simple and effective way to evaluate the polarization and dielectric relaxation behaviors of ferroelectric nanocrystals/polymer systems. (C) 2016 Elsevier B.V. All rights reserved.