Crystal, electronic structures and the magnetic and electromagnetic wave absorption properties of BaFe12-xCoxO19 (x = 0-2) M-type hexaferrites prepared by a co-precipitation technique were studied. The analyses of X-ray diffraction patterns indicated that the samples mainly crystallized in the P6(3)/mmc hexagonal structure, with the additional constitution of Y-type hexaferrite as x > 0. The replacement of Co(2+ )for Fe3+ in BaFe12-xCoxO19 changed the lattice constants and caused lattice distortions. Particularly, Co2+ doping also reduced magnetization and hard magnetic property of BaFe12-xCoxO19. This is ascribed to magnetic moment of Co2+ smaller than that of Fe3+ and to the decrease of magnetocrystalline anisotropy. Having studied electromagnetic wave absorption properties in the frequency range f = 0.1-18 GHz, we found BaFe(12-x)Co(x)O(19 )showing high reflection loss (RL) values at frequencies of 0.1-15 GHz, but fairly low RL values at higher frequencies. These features suggest that BaFe12-xCoxO19 can be suitable to electronic devices working at GHz frequencies.