We have measured the unpolarized and polarized emission spectra of 4I9/2?4I15/2 (810nm) and 4S3/2?4I13/2 (860nm) electronic transitions of Er3+ in LiNbO3 crystal under different incident directions and polarization states of excitation beam. From the measured emission spectra, the emission and absorption cross-section spectra were calculated based upon McCumber theory. It is found that Er3+ electronic transition shows interesting excitation beam direction effect in polarization dependence, spectral shape, and cross-section value. Both transitions are highly p-polarized as the excitation beam was aligned perpendicular to the optical axis of crystal while being highly s-polarized as the excitation beam was oriented parallel to the optical axis of crystal. The spectral shape in the case of the perpendicular excitation is very different from that in the case of parallel excitation. The cross-section value in the perpendicular excitation case is at least 1.5 times larger than that in the parallel excitation case. These excitation direction effects are independent of the polarization state of excitation light, and are attributed to the selective Er3+ site excitation. In addition, the Er3+ 860nm emission lifetime was measured to be 27 +/- 5 mu s and the quantum efficiency of the emission is 2.5%.