Compatibility property, as well as crystalline morphology, of NBR/PEO blends has been investigated by Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), X-ray diffraction (XRD), and polarized optical microscopy (POM) thoroughly. There is no apparent shift of nitrile or ether groups in the FTIR spectra of NBR/PEO blends. Based on the calculations from glass transition temperature, the maximum volume fraction of PEO dissolved in NBR phase is about 6.41 % in blend with 5 wt% PEO content (PEO-5), indicating a weak intermolecular interaction in the NBR/PEO blends. From the characteristic absorption bands in the FTIR spectra, XRD and POM graphs, the crystallinity ratio of NBR/PEO blends decreases as the NBR content increases, which is further proved by DSC measurement that the crystallinity ratio and crystal melting temperature of pure PEO are 82.6 %, 69.9 A degrees C, and that of PEO-5 are 16.9 %, 59.5 A degrees C. This illuminates that the weak intermolecular interaction will affect the crystallinity ratio and crystal melting temperature of the NBR/PEO blends.