In the spectroscopic analysis of composite elements by x-ray fluorescence (XRF), it is the fundamental feature of this method that the background x-ray intensity is lower than that with electron excitation. However, the background x-rays of this method, which consist of Thomson (Rayleigh) and Compton scattered x-rays from the primary radiation, impair the analytical performance at the ppm level. In order toinvestigate the intensity of the background x-rays precisely,the study was conducted in two parts. The first part compared the measured and theoretically calculated x-ray intensities for Rh Kα and Rh Kβ peaks from various materials. The second part examined the determination of low concentrations of lead,arsenic and colonium in steel samples. The variation in the background x-ray intensities of the analyzed elements was found to be caused by the variation of the major elements and a correction equation for it is derived.