Fused borate glass beads were used for the determination of 42 components (Na, Mg, Al, Si, P, K, Ca, Se, Ti, V, Cr, Mn, Fe Co, Ni, Cu, Zn, Ga, As, Rb, Sr, Y, Zr, Mb, Sn, Cs, Ba, La, Ce, Pr, Nd, Sm, Gd, Dy, Er, Yb, Hf, Ta, W, Pb, Th, and U) in felsic rocks using x-ray fluorescence spectrometry (XRF). Low-dilution glass beads with 1:1 sample-to-flux ratios (called 1:1 glass beads) were prepared using the double-fusing method to measure Se, Sn, Cs, Hf, Ta, and rare earth elements. Double-fusing, which uses two heating stages with intervening cooling to room temperature, was used to prepare homogeneous 1:1 glass beads. Pulverized rock samples of less than 20 μm modal diameter enabled us to prepare homogeneous 1:1, 1:2, and 1:10 glass beads. The glass bead thickness was set as constant because the fluorescent x-ray intensity of heavier elements, such as Rb, Sr, Y, and Zr, was influenced by thickness of 1:10 glass beads. Mutual interference of the nine analytical lines, V Kα, Cr Kα, Y Kα, Zr Kα, Nb Kα, Ba Lα, Ce Lα, Er Lα, and Yb Lα, was corrected using the intensities of Ti Kα, V Kα, Rb Kα, Sr Kα, Y Kα, Rb Kα, Ba Lα, Zr Kα, and Ni Kβ, corresponding to each overlap. Calibration curves of the 42 components showed good linearity (coefficient of determination, r = 0.991-1.000). The calibration ranges, indicating lower and upper limits of detection, were 1.6-58 to 0.03-7.6 mass ppm for the major elements (Na2O, MgO, Al 2O3, SiO2, P2O5, K 2O, CaO, TiO2, MnO, and Fe2O3) in 1:10 glass beads, 0.2-0.5 to 50-100 mass ppm for Rb, Sr, Y, and Zr in 1:10 glass beads, 0.3-6.0 to 20-230 mass ppm for minor elements (V, Cr, Co, Ni, Cu, Zn, Ga, As, Nb, Ba, W, Pb, Th, and U) in 1:2 glass beads, and 0.7-8.9 to 20-220 mass ppm for trace elements (Sc, Sn, Cs, Hf, Ta, and rare earth elements) in 1:1 glass beads. Using this method, we determined 42 components in two granites from Japan, weathered granite, obsidian, and rhyolite.