In this article, polyimide (PI) films were fabricated via the three-step method including the reactions of condensation polymerization, chemical imidization, and thermal imidization. In comparison with the conventional two-step method to produce PI films, there was an additional step in the present method, i.e., chemical imidization. The aim of chemical imidization was to get PI intermediates with different pre-imidization degree (pre-ID). And PI component in PI intermediates acted as in-situ rigid-rod segments and induced orientation in the films of PI intermediates. Then the orientations of molecular chains were preserved in the following thermal imidization, and caused the difference in aggregation structure and property of the final PI films. The test results indicated that the orderly degree of molecular chains and mechanical properties of PI films increased with pre-ID increasing. Furthermore, this tendency was much more obvious for more rigid backbone structure. (c) 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013