Liquid crystal molecules on a rubbed polymer alignment layer are oriented at some polar angle away from the surface. This so-called pretilt angle is an important parameter which determines the electro-optical properties of liquid crystal devices. Therefore, there is a necessity to deeply study generation of pretilt angle and its stability. Several researchers study on this problem but the physical mechanism is not thoroughly understood. Therefore, we have investigated LC pretilt angle and polymer inelination angle and the effect of heat treatment about these angles. We have also studied the relation between LC materials and their pretilt angles as well as the effect of the heat treatment on them. From these results we discuss the mechanism of change in LC pretilt by the treatment.