The irradiation effect of 0.45‐MeV protons on the solubility and diffusivity of interstitial impurities has been studied by annealing nitrogen‐implanted molybdenum samples in the temperature region 600–800 °C. The nondestructive (p,&ggr;) resonance‐broadening method was applied as a probe for the nitrogen. Even for the low proton irradiation doses, a remarkable increase in solubility and a decrease in diffusivity were observed.