The influence of orientational Kerr effect on photo-induced alignmetnt of liquid crystals was studied at different intensities of linearly polarized 355nm laser pulse and viscosities of the photo-prepolymer layers. The coumarin photo-prepolymer materials(LPP-2) which was used to make linear photo-polymerization(LPP) layers has large third order nonlinearity at 355nm laser pulses with 250ps(FWHM) duration. Its nonlinear refractive index was

n

2

=-2.37×10

-9

esu. The major origin of its third order-nonlinearity is orientational Kerr effect. The polarized microscopic photographs of liquid crystals cells obtained at different irradiation intensities and viscosities certainly exhibit that orientational Kerr effect increases the probability of linear photo-polymerization in the linear polarized direction and improves the quality of photo-induced alignment of liquid crystals.