Two kinds of hot-pressed B⁴C specimens were irradiated with 15MeV He⁺ from 4.3×10¹⁴ to 1.13×10¹⁶ion/cm² at 400–760 °C, and with 100keV He⁺ from 1.0×10¹³ to 2.0×10¹⁷ion/cm² at room temperature. After ion irradiation, the microstructure of specimens was analyzed by transmission electron microscopy (TEM). The ion-irradiation by 15MeV helium ions produced a radiation-enhanced precipitation with Fe-rich composition and the radiation-induced amorphization in the B⁴C matrix, but the irradiation by 100keV helium did not make amorphization. This result suggests that the inelastic scattering (electron excitation), rather than elastic scattering, plays an important role in amorphization of B⁴C. The annealing of ion irradiated B⁴C above 1000°C indicated incineration of precipitated crystals and a formation of a small numbers of helium bubbles.