The orientation of the crystalline lattice formed as a consequence of strain-induced crystallization (SIC) was revisited for a natural rubber (NR) sheet undergoing planar elongation by being stretched in one direction while keeping the other dimension unchanged. For this purpose, two-dimensional wide-angle X-ray diffraction patterns were measured by changing the inclination angle of the incident X-ray beam to the specimen sheet. The intensity of the reflection from the (120) plane of the orthorhombic crystal increased with increasing inclination angle from the normal direction of the specimen sheet; this result indicated that the orientation of the (120) planes was parallel to the surface of the specimen sheet. Moreover, the intensity of the (200) plane reflection reached a maximum at a slightly inclined angle from the normal of the specimen surface. WAXD measurements were also conducted using different X-ray wavelengths (0.06, 0.10, and 0.15 nm) to evaluate the inclined angle of the acplane with respect to the surface of the specimen. By changing the X-ray wavelength, the distribution of reciprocal lattice points was altered such that the inclined angle of the incident X-ray beam to the specimen sheet needed to be changed to meet the diffraction condition. The inclined angle at the maximum intensity of the (200) reflection increased as a function of the X-ray wavelength. Based on this result, the preferential orientation of the acplanes was determined, whereby the acplane was not completely parallel to the surface of the specimen sheet but was slightly inclined by 6.4°. Thus, a dual orientational state was deduced. Therefore, the preferential orientation of the acplane was nearly parallel to the surface of the specimen sheet, with the inclined angle ranging from 6.4° to 19.6° within the volume of the specimen irradiated by the incident X-ray beam.