Quantitative chemical analysis of rock-forming minerals was tried by using the EDX type EPMA-an energy-dispersive X-ray spectrometer (EDX : Philips EDAX DX-4) with a scanning electron microscope (SEM : JEOL JSM-5400)-in Faculty of Integrated Arts and Sciences, Hiroshima University. The accuracy of analytical data is almost agree with those by the reference methods of wave-length dispersive X-ray microanalysis using WDX type EPMA and the recommended values for elements with more than 1 wt%.0 On the other hand, the standard deviation of the measurments for elements with more than 0.5 wt 0s two times as much as that by the WDX type EPMA. These results are concordant with previous studies using different EDX type EPMAs. It can be synthetically concluded that our EDX type EPMA has accuracy and precision enough for practical usage on analysis of major elements in rock-forming minerals.