Poly(amide acid) labeled with perylenetetracarboxydiimide (PEDI) was prepared from 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA), p-phenylenediamine (PDA), and dianiino-PEDI. Poly(amide acid) was then reacted with sodium hydride and various kinds of alkyl iodides for transformation into various poly(amide ester)s. The cast films were imidized while fixed on glass substrates to give BPDA/PDA polyimide films. The degree of in-plane molecular orientation (f) of the polyimides and their precursors, poly(amide acid) and poly(amide ester)s, were determined via measurements of the visible dichroic absorption at an incidence angle for a rodlike dye (PEDI) bound to the main chain. All precursor films showed relatively low degrees of in-plane orientation. After imidization of the precursors fixed on glasses, however, striking spontaneous in-plane orientation behavior was observed. The f value for polyimide film from a poly(amide acid) precursor was as high as 0.7-0.8. The f value for polyimide film from a methyl ester precursor, however, was lowered to 0.4-0.5, but it increased with the increasing size of the alkyl. groups. Good correlations of the in-plane orientation of the polyimide films with the tensile modulus of the films and the in-plane orientation of the graphitized films were observed.