Fe²⁺:Fe³⁺ ratios of natural fayalite and forsterite were estimated by applying a correlation between Fe²⁺:Fe³⁺ ratios and relative intensities of FeL_α and FeL_β X-ray emission peaks. These ratios were then compared to those determined by the Mössbauer spectroscopic method to examine the consistency between the two methods. Average Fe²⁺:Fe³⁺ ratios of the fayalite and forsterite obtained from the X-ray emission peak intensities were 94(3):6(3) (n = 3) and 90(3):10(3) (n = 3), respectively. These values were close to those determined by Mössbauer analysis: 94(3):6(1) and 94(4):6(1) for fayalite and forsterite, respectively. The X-ray emission peak intensity method is thus useful for the estimation of Fe³⁺ content in olivine.