The rf impedance characteristics of a spherical probe, which is immersed in a warm magnetized plasma, are investigated theoretically. Both grid and solid sphere models are treated. The fluid model is used to describe the magnetized electron plasma. The impedance contains a resistance resulting from the radiation of electrostatic plasma waves. The resonance frequency for the warm magnetized plasma, at which the reactance vanishes, is different from the electron cyclotron frequency, at which the resonance occurs in a cold magnetized plasma; it depends on both the radius of the sphere and the Debye length. Several previous theories, which have been studied, are unified in the present theory. It is also found that the surface charge density on the sphere is exactly uniform in the cold magnetized plasma.