Abstract: Color reactions of rare earths with high sensitivity and selectivity based on the formation of polycomponent complexes in the system of RE-amino-J acid chlorophosphonazo-TPC-C₂H₅OH have been investigated. In acid medium (0.1-0.3N HCl) in the presence of cationic surface-active agent TPC and ethyl alcohol, amino-J acid chlorophospho-nazo with rare earths reacts to form blue colored complexes.The maximum absorption of the complex of cerium was observed at 695nm. The molor absorptivity of the complex of cerium was 2.01×10⁵ 1^-1. mol-1. cm^-1. Under the same condition, heavier rare earths do not convert to corresponding complexes. The color remains stable for 1 hr. Beer's law is obeyed over the range 0-12 μg/25ml Ce. Many cations and ani-ons do not interfere. The method has been applied to the determination of RE in steel and the results of determination are found to be satisfactory.