Abstract: An isotope dilution spark source mass spectrometric method (ID-SSMS) is de-veloped for the certification of trace elements in U_3O_8 standard reference material.The advantages of this method are:(a) high sensitivity and simple sample prepa- ration; (b) simultaneous determination of many elements; and (c) measurementsindependent of calibration standard and providing results of precise absolute ana-lysis. A detailed study is preformed for selections of the interferencelines,the opti-mum dilution condition and the conducting medium. In applying this method forthe certification of the trace elements Mo, Cu,Fe,Ca,Pb,Ba, K and Zn in domes-tic U_3O_8 standard reference material, the determined concentrations in the sampleare in good agreement with the medium values. The average of all relative stan-dard deviations is ±11%.