Through preliminary experiments, we found that at pH 5.6 malic aoid hag a much more powerful masking action towards the light rare earths than lactic acid and glycerin acid.It was found that only malic acid can displace EDTA from the RE-EDTA complexes quantitatively.In this way, 40-1000μg of Ce(Ⅲ) or 50-500μg of the mixed light rare earths can be so titrated spectrophotometrically with 0.002 M lead nitrate solution using xylenol orange as indicator, while over 20 kinds of canons do not interfere.This method is highly selective and seems possible to be used in the titration of rare earths in minerals or in iron and steel samples with preliminary separations.