Tilt angles of nematic liquid crystal molecules, 5CB, have been investigated in cells with rubbing-free aligning layers of polyimide Langmuir-Blodgett (LB) films on the aluminum electrodes using the attenuated total reflection (ATR) measurement. The ATR properties were evaluated from the surface plasmon polariton and the guided wave excitation modes when various DC voltages were applied to the cell. The tilt angles near the aligning layers of the polyimide (Pl) LB films and in the middle layer of the cell were calculated by fitting the theoretical ATR curves to the experimental ones. This technique is very useful for evaluating aligning properties of liquid crystal molecules on LB films in the cells.