The effect of gamma irradiation and electron irradiation on the crystal structure and magnetic properties of barium hexaferrite BaFe12O19 (solid-phase synthesis) was studied. Irradiations caused changes in the ratio of crystalline phases and crystallite sizes, which resulted in changes in the main parameters of the hysteresis loop: coercive force, residual magnetization, saturation magnetization. These characteristics change nonmonotonically with varying dose, especially immediately after irradiation. In particular, the saturation magnetization measured at 300 K after γ-irradiation of the sample with a dose of 2.1 × 107 R decreased from the initial value of 52.5 to ∼40.2 emu/g.