We present a study on radiation losses in the microwave X band in Al-Cr substituted Y-type hexaferrites,namely Ba2Mg2Alx/2Crx/2Fe12-xO22 (x =0,0.5 and 1.0).The study is performed by means of a vector network analyzer,Fourier transform infrared spectroscopy,a vibrating sample magnetometer and x-ray powder diffraction.Ba2Mg2Fe12O22 hexaferrite shows radiation loss of-37.25 dB (99.999％ loss) at frequency 9.81 GHz,which can be attributed to its high value of saturation magnetization,i.e.,22.08 emu/g.Moreover,we obtain that magnetic properties have strong influence on the radiation losses.