Abstract: In a B-R buffer medium of pH 3.0,a colored compound complex was formed between protein and the binary complex of Eu(Ⅲ)-p-Acetylcarboxylazo-p (abbreviated as Eu(Ⅲ)-pA-p),having its absorption maxima at the wavelength of 695 nm,with a bathochromic shift of 145 nm from the absorption maxima of Eu(Ⅲ)-pA-p complex.Based on this color reaction,the binary complex,Eu(Ⅲ)-pA-p,was used as a photometric probe for the determination of protein in biological samples.Calibration curves for determination of BSA and HAS were prepared and linear relationships between the absorbancy values and concentrations of protein were obtained as follows:for BAS 0.010-0.030 g·L-1 (r=0.995 4) and for HAS 0.005-0.025 g·L-1 (r=0.994 7).In the determination of total protein in two biological samples,RSD′s (n=5) of the results obtained were less than 6.5%,and recoveries were in the range of 98.4%-103.7%.