In the present work, barium hexaferrite nanoparticles were synthesized through a co-precipitation route in the presence of a high concentration hydroxide ion at low temperature. The effect of annealing temperature on structure, morphology and magnetic properties of nanoparticles was investigated by x-ray diffraction (XRD), Fourier transform infrared (FTIR), field emission scanning electron microscopy (FE-SEM), and vibrating sample magnetometer (VSM). XRD pattern of the samples along with FTIR analysis confirmed the formation of crystalline hexagonal ferrite phase for powders annealed above 700°C. The FE-SEM images showed that the particle size increased from few nanometers to micrometers by elevating the annealing temperature from 90 to 1200°C. The VSM results revealed that by increasing annealing temperature magnetization and coercivity increased and reached the maximum value of 46emu g -1 and 5278Oe, respectively, for the sample annealed at 900°C. Also, the low-temperature (90°C and 500°C) annealed samples were superparamagnetic at room temperature, due to their near-zero coercivity and remanence. In the second part of project, the effect of Ce doping on structural and magnetic properties of nanoparticles was investigated. XRD pattern of the samples along with FTIR analysis confirmed the formation of crystalline hexagonal ferrite phase at 1100 o C.The magnetic properties of samples indicate that with the Ce doping the saturation magnetization (M s ) and coercivity (H c ) show increasing- decreasing behavior and the magnetic properties of BaFe 12 O 19 improved by Ce doping. Moreover, Cesubstitutanthave special effect on microwave absorbance in barium place.