Co0.5Ni0.5Fe2O4 nanofibers with 70-100nm in diameter were fabricated by the electrospinning and calcination process. Their saturation magnetization gradually enhances from 37.5 to 66.2 emu/g with increasing calcination temperature from 450 to 800 degrees C, while the corresponding coercivity increases initially, achieving a maximum value of 78.3 kA/m at 600 degrees C and then decreases with further increase in calcination temperature due to the transformation of magnetic structure from single-domain to multidomain. By dispersing the nanofibers into a silicon rubber matrix homogeneously, the electromagnetic parameters of them were measured in the frequency range of 2-18GHz and the microwave reflection loss was calculated according to the transmission line theory. The reflection loss exceeding -5dB is obtained between 11 and 18GHz for the silicon rubber composites containing 15 vol% Co0.5Ni0.5Fe2O4 nanofibers with coating thicknesses of 2.5-3.2mm. These Co0.5Ni0.5Fe2O4 nanofibers possess a good microwave absorption performance in the Ku band and have a great potential as microwave absorber for practical applications. (C) 2012 Elsevier B.V. All rights reserved.