In this paper, barium hexaferrite thick films with thickness of 80 microns were prepared on alumina substrates by screen printing method for applications in self-biased planar microwave devices. The influences of sintering temperature on the microstructures and magnetic properties of barium ferrite (BaM) thick films were investigated. The results show that with the increase of sintering temperature, the grain size increases and the porosity of the BaM thick films decreases. When the sintering temperature is below 1200 °C, the BaM thick films show magnetic properties with coercive force of about 3.5 kOe and magnetization at 20 KOe (4πM20kOe) of about 1750 Gs. When the sintering temperature is greater than 1200 °C, the magnetic properties deteriorate remarkably and exhibit a coercive force of 0.4 kOe and 4πM20kOe of about 480 Gs due to the over-sintering and diffusion of Al atoms into the BaM thick films. A new non-ferromagnetic phase Al13Ba7 is formed, which is detected by XRD.