The tilt angles of liquid crystal molecules, 5CB, have been investigated in liquid crystal cells with rubbing-free aligning layers of polyimide (PI) Langmuir-Blodgett (LB) films on aluminum electrodes using the attenuated total reflection (ATR) measurement method. The surface plasmon polariton (SPP) and/or the guided wave excitation modes (GWEM) were observed in the ATR curves of the liquid crystal cells when various DC voltages were applied to the cell. The ATR properties were evaluated from the SPP and the GWEM. The tilt angles of the liquid crystal molecules were calculated by fitting the theoretical ATR curves to the experimental ones using various models of the liquid crystal layer structure. Furthermore, the electric field intensities in the cell were calculated at several incident angles in the ATR curves. The ATR measurement is very useful for evaluating the alignment properties of liquid crystal molecules in liquid crystal cells.