The extraction of Yb3+ from chloride solution has been studied using mixtures of bis(2,4,4-trimethylpentyl)phosphinic acid (Cyanex272) and 2-ethylhexyl phosphinic acid mono-2-ethylhexl ester (P507). The results show that Yb3+ is extracted into heptane as YbA(3)(HA)(3) with Cyanex272, YbL3(HL)(3) with P507, and YbA(2)L(4)H(3) with synergistic mixture. The equilibrium constants, formation constants, and thermodynamic functions have been determined. Extraction mechanism and extraction process are also proposed. The extraction of heavy lanthanide ions by mixtures of Cyanex272 and P507 is studied and the possibility of separating heavy rare earth ions is discussed.