We have developed Ti/Au bilayer transition-edge sensor (TES) microcalorimeters for future X-ray astrophysical satellite missions such as DIOS. One possible concern on the space use of TES microcalorimeters is its radiation tolerance. We have evaluated the performance of a Ti/Au bilayer (30/40 nm thick) TES microcalorimeter with 1.5 m thick Au absorber, before and after irradiation of 150 MeV proton beam with a total dose of 10 krad, corresponding to 10 years in the low Earth orbit. No significant changes on transition temperature, sensitivity, normal resistance, and critical current were observed. The energy resolution for 5.9 keV X-rays was 5.6 0.3 eV (FWHM) after the irradiation, which was slightly worse than 5.1 0.3 eV before the irradiation. We consider that our TES has sufficient radiation tolerance in orbit.