In recent years, for the development of magnetic tape, it has become increasingly important that the elemental content be determined accurately and rapidly. In the past, the elemental content of magnetic tape was determined by calibration analysis using a wavelength dispersive X-ray fluorescence spectrometer(WDXRF). For calibration analysis many standard samples and large amount of sample were needed. Preparation of sample for calibration analysis, as well as for inductively coupled plasma emission spectral analysis(ICP) was difficult. On the other hand, for thin layer fundamental parameter analysis(we call TLFP) using a WDXRF, a few standard samples and l.pss sample are needed and preparation of the sample is easy. The superiority of TLFP analysis can be seen In comparison with calibration analysis and IOP analysis in Table 1. For this reason, this study has established a method for accurate and rapid determination of the elemental composition of oxide magnetic tape by TLFP analysis using a WDXRF.