Co2Y-type hexaferrites (Ba2CuxCo2-xFe12O22, x=0,1) have been fabricated by the conventional ceramic process. The complex permittivity and permeability of Co2Y hexaferrite composites have been measured using a vector network analyzer in the frequency range of 2-18 GHz. The results show that Co2Y hexaferrite composites have a high permeability and a low permittivity. This can be adjusted by a CuO additive and particle sizes. The reflection loss (RL) values of Co2Y hexaferrite composites backed with a conducting plate indicate that the composites possess good microwave-absorbing properties. The minimum RL value of the composites was below -30 dB. The microwave-absorbing materials with 10 GHz (8 GHz) bandwidth for attenuation of 5 dB (10 dB) can be achieved.