In this paper Polyglycol (PG) was used as ‘soft’ template to induce the polymerization of aniline in aqueous ethanol and hence control both the nucleation and growth of polyaniline (PANI) nanofibers. The products were characterized by Transmission electro microscope (TEM) and X-ray diffraction (XRD) techniques. TEM photos showed that the diameter of PANI nanofibers synthesized in pure water is 100nm while that of PANI nanofibers synthesized in aqueous ethanol is 50nm. It revealed that the volume fraction of ethanol showed really important effect on the morphological parameters of the PANI nanofibers. The X-ray diffraction patterns of the PANI nanofibers showed high crystallinity. Moreover, the resulting PANI nanofibers exhibited an unusual electromagnetic loss at the microwave frequency (f = 8.2~12.4 GHz) . Compared with 1.79, the highest electrical loss, tanδe, of the microparticles PANI at 8.47 GHz and 0.72, the highest magnetic loss, tanδm at 10.93 GHz, it was noted that the highest electrical loss, tanδe, of PANI nanofibers reached 3.26 at 10.4 GHz, and the highest magnetic loss, tanδm, was 2.85 at 9.35 GHz. It might arise from order arrangement of polaron as charge carrier caused by nanofibers morphology and can be used for the potential application as microwave absorbing materials.