X-ray spectrometric determination of $Ta_2O_54, $Nb_2O_5$ and $ZrO_2$ in tin-slag samples using the double dilution technique was conducted. Tin-slag samples and one synthesized standard sample having similar composition to the samples were diluted with anhydrous $Li_2B_4O_7$ at the level of 1.00, 2.00 and 3.00% of the sample content, respectively. The diluted samples were fused at $1,150^{circ}C$ for 30 minutes, and these glass beads were finely ground and pelletized. With the X-ray intensities measured, analytical results were calculated by the double dilution equation. The results agreed to the reference values obtained by the standard calibration method and the simple dilution technique within allowable error range and were reproducible.