Preliminary experiments on the accuracy of quantitative microprobe analysis for the instrument set in the Institute for Themal Spring Research, Okayama University were carried out. Dead time of the instrument ranged about 5.5-5.6 microsecond, which delayed 1.5 microsecond than usual value. Bombarding by finely focused electron beam, intensities of the characteristic X-ray of alkali metal such as NaKα and KKα decreased drastically in five to ten minutes. Intensities of the characteristic X-ray decreased in relation to the degree of off-focusing, when the spectrometer fixed at optically focused position. Readjusting of spectrometer after every move of sample was indispensable for the proof of accurate intensities. Applying BENCE and ALBEE'S correction method, empirical a factors was approved of preferable for quantitative analyses of silicates than calculated α factors.