Abstract The x-ray fluorescence spectrometer (XRS) on board Japanese lunar polar orbiter SELENE (Kaguya) will provide global distribution of major elemental composition on the lunar surface in energy range of characteristic K-α x-ray line emission for Mg, Al, Si, Ca, Ti, and Fe. These measurements will contribute to research of lunar origin and its evolution. The XRS shows a good energy resolution within 200 eV at 5.9 keV relying on charge coupled device (CCD) as photon energy dispersive detector. Total collective area of 100 cm² for main detector facing the lunar surface is composed of 16 CCD chips. Instrumentation of the XRS and its performance evaluated in laboratory are presented.