Rubbing-induced molecular aligement on an alkyl-branched polyimide film with varying unidirectional rubbing strength has been investigated with the use of optical phase retardation measurement, atomic force microscopy (AFM), and second-harmonic generation (SHG). Our AFM images suggest that the rubbing- induced micro-groove should play a minor role in aligning liquid crystal (LC) molecules. The polar angle of the polar head group of a LC monolayer on an alkyl-branched polyimide film was found to vary with the rubbing strength. The results obtained from various experimental techniques can be reconciled with a simple molecular model proposed in this paper.