AbstractElastic moduli of the crystalline regions in high polymers have been studied. Oriented specimens were used throughout. Lattice strains were measured by an x‐ray technique in the direction of the fiber axis as well as in that perpendicular to the fiber axis. The moduli for both directions were calculated on the basis of the assumption that the stress is homogeneous within a specimen held under a load. Remits obtained for various kinds of polymers were discussed in terms of the crystal structures of the polymers, pan icularly the skeleton conformation and the cross‐sectional bulkiness of the chain molecule in the crystal. It was shown that the moduli in the direction of the fiber axis are widely different depending upon the polymer. They vary from 240 × 104kg./cm.2for polyethylene to 4.1 × 104kg./cm.2for isotactic poly (vinyltert‐butyl ether). In the direction perpendicular to the fiber axis, the moduli were shown to take values within a narrow range of magnitude, 3–9 × 104kg./cm.2. Some of these moduli were compared with the calculated values reported by several authors. To find experimental support for the assumption of the homogeneous stress, measurements were made by using several oriented specimens of different fine textural structures. Inherent values of the lattice moduli were obtained, regardless of the specimens used, which gives a strong support for the