A new heteronuclear complex, rare earth (III)-copper (II)-m-trifluomethyl chlorophosphonazo (CPA-mCF3) system for determining trace rare earth ions is presented. In a medium of 0.02mol/L NH4Cl,1. 0×10−3mol/L Cu(II),1.0×10−5mol/L CPA-mCF3, a very sensitive polarographic adsorptive wave is observed by using a single sweep oscillopolarograph at about –0.83V (vs. Ag/AgCl). The linear relationship between the peak current and the concentration of rare earth exists from 6. 0×10−9to 1. 0×10−6mol/L. The detection limit of rare earth is down to 2. 0×10−9mol/L for Tm3+. This method has been applied to determine trace RE in several samples of Chinese tea. The results are satisfactory. The composition of the complex is detected as RE (II): Cu (II): CPA-mCF3= 1: 1: 2.