Abstract The effects of 200 MeV proton irradiation on the magnetic flux of Nd–Fe–B and Sm–Co magnets have been investigated over the dose range from ∼10 2 Gray to ∼2×10 5 Gray. Nd–Fe–B magnets with coercive force H cj 1.15 MA/m and 2.5 MA/m were used as samples, where their permeance coefficient P c was 0.5∼2.0. The magnetic flux of Nd–Fe–B magnets decreased as the proton dose increased, while the flux of Sm–Co magnet did not change. The relation between the flux loss Δ Φ of Nd–Fe–B magnets and the absorbed dose D was expressed as Δ Φ =− η log D +const., where value η was 39±3% with D in Gray. The absorbed dose D 20 , which caused the flux loss of 20%, was 5.1×10 2 Gray for P c =0.5,2.0×10 3 Gray for P c =1.0, and 6.8×10 3 Gray for P c =2.0 in case of Nd–Fe–B magnets with H cj =1.15 MA/m. The dose D 20 was 2.3×10 4 Gray for P c =0.5, and 2.9×10 5 Gray for P c =2.0 in case of Ne–Fe–B magnets with H cj =2.5 MA/m. Increase of both of permeance coefficient and coercive force led to the enhancement of the resistance to the radiation-induced damage.