We present an anomalous electro-optic effect in polar liquid films: liquids, usually considered to be isotropic, possess the linear electro-optic effect that occurs only in materials lacking inversion symmetry. Due to the observed large effect in the low-frequency range and slow response speed, this strange effect was thought to come from the field-induced orientation of large mass. Therefore, we brought forward a physical model that contributed to the interpretation of this phenomenon: field-induced pre-oriented, short-range orderly dipole clusters in liquid films break the macroscopic symmetry and results in this asymmetric effect. Finally, combined with spectral analysis, the formation of clusters induced by an electric pulse was proved.