Microwave irradiation can cause high local temperatures at supported metal nanoparticles, which can enhance reaction rates. Here we discuss the temperature of platinum nanoparticles on γ-Al2O3 and SiO2 supports under microwave irradiation using the Debye–Waller factor obtained from in situ extended X-ray absorption fine structure (EXAFS) measurements. Microwave irradiation exhibits considerably smaller Deby–Waller factors than conventional heating, indicating the high local temperature at the nanoparticles. The difference in the average temperatures between the platinum nanoparticles and the bulk under microwaves reaches 26 K and 132 K for Pt/Al2O3 and Pt/SiO2, respectively. As a result, Pt/SiO2 exhibits considerably more reaction acceleration for the catalytic dehydrogenation of 2-propanol under microwave irradiation than Pt/Al2O3. We also find microwaves enhance the reduction of PtOx nanoparticles by using operando X-ray absorption near edge structure (XANES) spectroscopy. The present results indicate that significant local heating of platinum nanoparticles by microwaves is effective for the acceleration of catalytic reactions.