Radiation stability Of SiO2 antireflective film coated SiN and SiC x-ray mask membranes was studied. Although the transmission at 633 nm of the SiO2-coated SiN was reduced by about 8% after synchrotron radiation (SR) exposure with an absorber dose of 100 MJ/cm3, the oscillation of the transmission due to interference was considerably suppressed even after the SR absorption. Furthermore, the optical transmission spectrum of the SiO2-coated SiC was nearly equal to that of uncoated SiC after the SR absorption of 100 MJ/cm3. The pattern displacement induced by the SR absorption of 10 MJ/cm3 for the SiO2-coated SiN and for the SiO2-Coated SiC was sigma(x)=6 nm, sigma(y)=7 nm and sigma(x)=8 nm, sigma(y)=6 nm on the 25-mm-square area, respectively, the values of which were within the reproducibility of the displacement measurement. Electron spin resonance analysis indicated that no significant difference of spin density between the SiO2-Coated and uncoated SiN membranes was recognized before and after the SR absorption.