The structural changes in the uniaxial drawing process of an unoriented amorphous film of poly(ethylene naphthalene-2,6-dicarboxylate) (PEN) and in the heating process of an oriented amorphous film of PEN were studied using X-ray diffraction apparatus equipped with imaging plates. This apparatus allows us to record a time-resolved series of two-dimensional patterns of wide-angle X-ray diffraction in rapid succession, and, therefore, we can follow the structural changes during uniaxial deformation and/or thermal treatment processes. The results are as follows : (1) When an unoriented amorphous PEN film was stretched below T-g(=117 degrees C), it could be elongated up to a draw ratio (DR) of 4-5 via neck formation and became an oriented amorphous film. (2) In the heating process of the oriented amorphous film (DR=3.6, 65 degrees C), crystalline reflections started to appear near 120 degrees C, accompanied by streaks on the off-equatorial layer lines. The existence of these streaks on such layer lines indicates a lattice distortion due to the axial shift of neighbouring chains along the chain axis with respect to one another. Finally the film exhibited a fibre structure (transverse isotropy). (3) When an unoriented amorphous PEN film was drawn at 150 degrees C, the film exhibited a fibre structure accompanied by a lattice distortion that is similar to that mentioned above, and thereafter frequently showed so-called double orientation (uniplanar axial orientation : (($) over bar 110)[001]) in which naphthalene rings in the main chain are preferentially aligned parallel to the film surface despite the fact that the him was deformed in the mode of uniaxial free-width drawing.