In this study, we investigated the analytical performance of an energy dispersive X-ray fluorescence spectrometry (EDXRF) by measuring chemical compositions of eighteen standard rock samples covering compositional range of common igneous rocks. Glass beads were prepared and calibration lines for ten major oxides (SiO2, TiO2, Al2O3, Fe2O3, MnO, MgO, CaO, Na2O, K2O, P2O5) and eighteen trace elements (V, Cr, Co, Ni, Cu, Zn, Rb, Sr, Y, Zr, Nb, Cs, Ba, La, Ce, Nd, Pb, Th) were examined. We also prepared three original standard samples by mixing two standard rock samples in order to improve the accuracy of the calibration lines. Correlation coefficients of the calibration lines for major elements are better than 0.99 (except for Al2O3 with 0.95), and those for trace elements were between 0.96 and 0.99. The analytical accuracies for major and trace elements were almost compatible to those reported by the previous studies using a wavelength dispersive X-ray fluorescence spectrometry (WDXRF). The precisions of EDXRF are also comparable to those of WDXRF. The EDXRF analysis has become a useful and powerful technique to measure the chemical compositions of igneous rocks as well as traditional WDXRF.