Abstract: In a chloroacetate buffer medium of pH 3.0,both La(Ⅲ) and Ce(Ⅲ) ions gave highly sensitive color reactions with arsenazo Ⅲ,having their absorption maxima (λmax 657 nm) seriously overlapped and same linearity range of 0-1.0 mg·L-1.Chemometric methods of principle component analysis (PCA) and partial least squares (PLS) were applied to above mentioned spectrophotometric method and made it possible to determined La(Ⅲ) and Ce(Ⅲ) individually and simultaneously in iron and steel samples.Relative errors of less than 10% were obtained in its application to the analysis of some simulated samples.