X-ray diffraction profile analysis was applied to the study of polymers by Buchanan and Miller for the first time in 1966 [l]. They used the double-peak Fourier analysis described by Warren and Averbach [2]. In the case of polymers, two peaks of different orders of diffraction are not so easy to record, Single-peak analysis has been developed by many people [3-7] but very few results have been reported for the deformed structure of polymers. In this work the fine structure of a series of deformed i-polypropylene (i-pp) films was studied by a single-peak profile analysis based on the data obtained from a special arrangement of samples in the diffractometer. The crystallinity and degree of orientation during deformation were also studied.