A low-loss flexible magnetic composite with Ni0.8Zn0.2Fe2O4 (NZO) ultrafine particles embedded in a thermoplastic polyolefin elastomer matrix was fabricated with extrusion technology. The electromagnetic and mechanical properties of the as-prepared composites were investigated in detail. The results indicate that as the volume of the ceramic fillers increased, the permittivity, permeability, and dielectric and magnetic loss of the composite all increased. The cutoff frequencies of the composites were all above 1 GHz. Because of the low resistivity of NZO, the dielectric losses of the composites were big and decreased with frequency below 100 MHz. Good frequency stability of the permittivities and permeabilities and low dielectric and magnetic losses within the measurement range were observed. All of the composites showed very good flexibility. With increasing volume of the ceramic filler, the tensile strength and elongation decreased. (C) 2009 Wiley Periodicals, Inc. J Appl Polym Sci 114: 3510-3514,2009