Abstract: Objective To detect protein in biological samples with lanthanum (Ⅲ)-chrome azurol S complex as a spectral probe.Methods In clark-lubs(KH₂PO₄-NaOH) buffer at pH 4-6, the absorbance at 478nm of lanthanum (Ⅲ)chrome azurol S complex decreases when adding prote in with in 30min at room temperature, and the decrease of absorbance is proportional to the concentration of proteins, which can be used to detect prote in.Results The calibration curve for bovine serum album in was linear up to 50 mg/L.The apparentmolar absorptivity of complex at 478 nm was 3.3×10⁵L/mol·cm and the complex was stable with in 4 hours.The detection limits of various proteins were 0.23-1.12 mg/L.The detection recoveries of album inuriaprote inuria and saliva were 92% and 105%, respectively, with a relative standard deviation of 1.8% (n=6).The common materials in organism had basically no interforrence.Conclusion The method can be applied to the determination of total amount of protein in biological samples with high sensitivity, better stability and anti-interfe rence.