Sum-frequency generation (SFG) vibrational spectroscopy and second-harmonic generation (SHG) were used to probe rubbed polyimide (PI) surfaces and liquid crystal (LC) monolayers adsorbed on them. The results show that rubbing preferentially aligns PI backbones along the rubbing direction, but has little effect on the side chain orientation at the surface. However, adsorption of an LC monolayer well aligned by the rubbed PI surface can cause the side chains to tilt towards the rubbing direction.