To assess the effects of proton beam on radiation sensitivity of the basidiospore and mycelium of oyster mushroom (Pleurotus ostreatus), the D₁₀ values and L₅₀ (lethal 50%) values were analysed. By the proton beam radiation, the survival rate and germination rates increased at the dose of 10 Gy~100 Gy and then decreased significantly over 500 Gy. L₅₀ values of basidiospore and mycelium of Pleurotus ostreatus were over 500 Gy and 400 Gy, respectively. D₁₀ values were calculated from linear regression formulae (D₁₀ = −1/slope(b), y = a + bx) as 750 Gy and 1,250 Gy, respectively. Based on our experiment, the optimum dose of proton beam as a mutation source would be between from 500 Gy to 750 Gy for basidiospores and from 400 Gy to 1000 Gy for mycelium of oyster mushroom.