We have demonstrated technique for measuring the third-order nonlinear optical susceptibility chi((3))(-3 omega;omega,omega,omega) based on internal reflection. Using this technique, we observed third-harmonic generation from a poly-DCH film deposited on oriented LB film of poly(3BCMU). Its chi((3)) was 2.1 times as large as an another film with no LB film. This suggests that the oriented LB film contributes to the alignment of the DCH monomer deposited on it.