Evaluation of uncertainty in the Energy Dispersive X-ray Fluorescence (EDXRF) spectrometric determination of platinum in alumina catalysts is discussed. Pressed pellets of the platinum standard and a catalyst sample were prepared by using microcrystalline cellulose powder as the base material. A linear calibration of the X-ray fluorescence spectrometer was obtained in the range of 0.1 –3mgg^-1 of platinum using pellets of matrix matched synthetic standards. The calibration function was obtained through bivariate least squares fitting, in conjunction with weighted regression of the residuals. The EDXRF results were compared with those obtained by instrumental neutron activation analysis and inductively coupled plasma optical emission spectrometry. Analysis of variance established the statistical parity of the results obtained by all the three techniques. A comprehensive evaluation of the various sources of uncertainty in the complete measurement process was carried out using a bottom-up approach. The main source of uncertainty was identified as the calibration of the EDXRF spectrometer, in which the major share was attributed to the intercept of the calibration function.