The effects of an external electric field and poly(methyl methacrylate) (PMMA) content on the crystallization of poly(ethylene oxide)(PEO)/PMMA blends were investigated using a polarizing microscope equipped with a hot stage and an external electric field supplier. The crystallization of PEO was strongly affected by the external electric field; i.e., the induction period increased and the crystallization rate decreased with the strength of the electric field. Since the magnitude of electric field effect was enormous, it was difficult to estimate the exact extent of the influence of the electric field on the crystallization of PEO, especially when the applied voltage was over 40 kV/cm. Blending PMMA with PEO decreased the crystallization rate of PEO and the influence of the electric field. Thus, it was possible to investigate the influence of the electric field over a wide range. The total crystallization rate of PEO in PEO/PMMA blends decreased as the strength of the external electric field increased. Because of the electro-inactivity of PMMA, the influence became progressively smaller as PMMA content increased. At higher PMMA contents, stronger electric field was needed to affect crystallization rates significantly