Abstract: A method of direct determination of aluminum,silicon,sulfur and vanadium in fuel oil by wave-length dispersion-XRFS was proposed.Matrix effect was corrected by applying the theoratical α coefficient and the internal standard methods.The sample was effectively homogenized by agitation in an ultrasonic water bath at 60 ℃ and 59 Hz for 45 min.Values of detection limit found for Al,Si,V and S were 1.0,0.9,0.7 and 0.6 mg·kg-1 respectively.Tests for precision were made by analyzing 2 known samples with 7 determinations,giving values of RSD′s in the range of 0.5% to 12.6%.The results obtained by analyzing 4 different fuel oil samples were found to be in consistency with the results obtained by the standard methods.