The effects of both rubbing force and rubbing density on polyimide alignment layers (ALs) and liquid crystal (LC) alignment were investigated, applying a wide range of pile impression and the number of rubbings. Weak rubbing creates inhomogeneous, partial modification of the AL, and in the region of weak rubbing reorientation of functional groups at the polyimide surface, orientation of the polyimide backbone along the rubbing direction, uniformity of LC alignment, pretilt angle, and azimuthal anchoring energy all increase with either pile impression (rubbing force) or the number of rubbings (rubbing density), showing a correlation between them. In the regime of strong rubbing where the AL gets sufficiently modified and the defect-free uniform alignment is thus achieved, the effects of rubbing force on these features are quite different from those of rubbing density, suggesting that the force and the density should be independently treated for the better characterization of the rubbing process. High-force rubbing further increases the modified surface area and surface polarity of the AL and consequently causes a decrease in pretilt angle and enhancement of both anchoring energy and thermal stability of pretilt angle, which doesn't occur for a greater number of low-force rubbings.