Epitaxial LiNbO3 films were grown on a-cut sapphire, i.e., α-A12O3(0112), substrates by pulsed laser deposition. It is found the oxygen pressure is an important deposition parameter to influence the orientations of the LiNbO3 films. At an oxygen pressure of 10−1 torr, LiNbO3(0001) film was grown epitaxially. And, at a low oxygen pressure (i.e., 5x10−4 torr), LiNbO3(1120) film was grown epitaxially. Due to the anisotropic electro-optic (EO) constants, these films with the different orientations display large differences in their EO properties: the epitaxial LiNb3(0001) film shows little EO effects, but the LiNbO3(1120) film shows a large quadratic EO behavior with an effective coefficient of 2.38×10−5 m2/V2. The dependence of EO effects on the orientations of the epitaxial films was analyzed in terms of the linear and quadratic EO tensors of LiNbO3.