The two different types of precursors, poly(amic acid) and polyisoimide, were prepared from 4,4'-(1,4-phenylenebis(1-methylethylidene))bisbenzenamine and 4-4'-oxydiphthalic anhydride for synthesis of polyimides. The FTIR spectroscopy was used to investigate the imidization reaction progress of poly(amic acid) and polyisoimide. Thermal properties were investigated using DSC and TGA. Stress behaviors during and after imidization processes of the two precursors were analyzed and compared using a bending beam curvature measurement system equipped with an in situ film thickness measurement system, the interferometer. The stress behaviors were significantly affected by the types of precursors, as water molecules evolved during the imidization process of poly(amic acid), being different from polyisoimide. They were also affected by temperature scanning rate for imidization and the annealing process.