One of the widely used techniques for earthquakes prediction research is radon concentration measurements within the seismo-active area. Radon concentration gradually grows during several months before a strong earthquake with a sharp increase few days before and abrupt drop few hours before the shock. This phenomenon usually is restricted to the region where the ground water trapped in the vicinity of the region of the earthquake, hollows out due to stress and escapes through the cracks developed. At the same time electromagnetic precursors exist showing the ionosphere modification before the earthquakes. One of them is the phase variations of the VLF signals passing over the region of anticipated earthquake. As it was shown by theoretical calculations this effect is connected with the changing of the conductivity of the Earth-ionosphere waveguide. The second effect is the ionosphere peak electron density variations. Scaled for particular local times (3 h, 6 h, 18 h LT) they show very high level of anticorrelation with the radon variations behavior.