Microwave and magnetic properties of single-crystal aluminum substituted barium hexaferrites BaAlxFe12-xO19 with Al substitution level x from 0 to 2 are reported. The single crystals were grown by the floating zone melting method. Films in the form of 100 μm thick, 1 mm wide, and 2 mm long resonators were used for ferromagnetic resonance (FMR) measurements in the frequency domain over 40–110 GHz for applied magnetic fields of 0–10 kOe. Based on these measurements, the hexaferrite parameters are determined. With increasing x from 0 to 2, the uniaxial magnetocrystalline anisotropy field increases from 17.88 to 33.68 kOe, while reasonable values of full FMR linewidth (35 Oe at 47 GHz and 140 Oe at 108 GHz) are maintained. These parameters ensure the potential for use of the ferrites in millimeter-wave devices.