A radioisotope-excited X-ray fluorescence analysis is applied for the determination of yttrium in xenotime ore. An annular109Cd source is employed for excitation of characteristic K X-rays of yttrium. The dilution method using pure starch as a diluent has been examined. Critical thickness of diluted ore sample has been determined. For the estimation of yttrium concentration in xenotime ore, the scattered radiation technique has been utilized. The validity and precision of the method have also been investigated.