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In this study, Al-doped ZnO particles are infiltrated into porous ZrSiO4 substrates to form an Al-doped ZnO/ZrSiO4 composite ceramic using sol-gel process. The doping of aluminum results in the high-concentration carriers, leading to the improvement of polarization capability and electric conductivity. When the Al content increases to 2.5 at.%, particle shape is changed from spherical into flower-like one, and the electric conductivity of ZnO/ZrSiO4 composite ceramics is further improved. Therefore, both dielectric loss and microwave absorption properties of ZnO/ZrSiO4 composite ceramics increase with the increase of Al content. The further increase of Al content leads to the production of ZnAl2O4, which is a low-permittivity ceramic, so the dielectric constant and dielectric loss of ZnO/ZrSiO4 composite ceramics show a decreasing tendency. Owing to the higher dielectric loss, the 2.5 at.% Al-doped ZnO/ZrSiO4 composite ceramics exhibit the best microwave absorption properties over the frequencies ranging from 8.2 to 12.4 GHz (X-band).