Although polyolefins are used extensively in the plastics industry, these polymers have found restricted use in electrospinning due to the limited number of solvents which provide reasonable solubility and dielectric constant. We have successfully prepared polyolefin fibrous membranes via electrospinning from multicomponent solvent systems. Fibers spun using a PB/PMP blend have a twisted-ribbon structure with irregular twisting points along the length of the fibers. The crystallization behavior was investigated by wide-angle X-ray diffraction, differential scanning calorimetry, and Fourier transform infrared spectroscopy. It was found that the crystallization of poly(1-butene) (PB) was strongly affected by the addition of poly(4-methyl-1-pentene) (PMP) to the blend. In pure PB fibrous membranes, a mixture of forms I and II were obtained, and the thermodynamically metastable form II gradually transformed into form I with aging at room temperature. However, this transformation did not occur in the PB/PMP blends, due to stabilization of the metastable form II of PB in the blend. Consequently, the rate of transformation (II -> I) of PB in the blend was retarded, whereas pure PMP fibers and fibers made from the PB/PMP blend both show PMP present in crystal form I, indicating that the crystallization behavior of PMP is not affected by blending.