The stability of Hg in an acrylonitrile-butadiene-styrene disk certified reference material (ABS disk CRM, NMIJ CRM 8116-a) during measurements by wavelength dispersion X-ray fluorescence (WD-XRF) analysis was evaluated in this study. The XRF intensities of Hg (L(α)) and Pb (L(α)) as well as the XRF intensity ratios of Hg (L(α))/Pb (L(α)) observed under different X-ray tube current conditions as well as their irradiation time were examined to evaluate the stability of Hg in the ABS disk CRM. The observed XRF intensities and the XRF intensity ratios for up to 32 h of measurements under 80 mA of X-ray tube current condition were constant, even though the surface of the ABS disk CRM was charred by the X-ray irradiation with high current for a long time. Moreover, the measurements on Hg and Pb in the charred disks by an energy dispersive XRF (ED-XRF) spectrometer showed constant XRF intensity ratios of Hg (L(α))/Pb (L(α)). From these results, Hg in the ABS disk CRM was evaluated to be sufficiently stable for XRF analysis.