The crystallization temperatures of Itokawa surface particles recovered by the space probe Hayabusa were estimated by a plagioclase geothermometer using sodic plagioclase triclinicity. The Δ131-index required for the thermometer, which is the difference in X-ray diffraction peak positions between the 131 and 13-1 reflections of plagioclase, was obtained by a high-resolution synchrotron Gandolfi camera developed for the third generation synchrotron radiation beamline, BL15XU at SPring-8. Crystallization temperatures were successfully determined from the Δ131-indices for four particles. The observed plagioclase crystallization temperatures were in a range from 655 to 660 °C. The temperatures indicate crystallization temperatures of plagioclases in the process of prograde metamorphism before the peak metamorphic stage.