Poly(amic dialkyl ester) precursors of high performance poly(4,4’-oxydiphenylene biphenyltetracarboximide) (BPDA-ODA) and poly(p-phenylene biphenyltetracarboximide) (BPDA-PDA) were synthesized and their thermal imidizations were investigated isothermally and nonisothermally by thermogravimetry. All precursors showed a two-step imidization behavior, fast imidization at early stage and slow imidization at intermediate and later stage. Kinetic parameters were estimated from the conversion versus time plots with the first-order rate equation. The imidization behaviors observed were interpreted with considering the T(g) variation, the natures of alkyl leaving group and precursor backbone, and the flexibility of polymer chain. In addition, the onset temperature of imidization and T(g) of precursors were estimated from the imidization kinetic data.