By combining the structures of P227 and Cyanex 272, a nonsymmetric dialkylphosphinic acid USTB-1 was synthesized. Its structure was confirmed by P-31 NMR, H-1 NMR, MS and IR. Its pK(a) and purity were determined through potentiometric titration method. Its extraction and separation performance for RE(III) were studied. The purity of USTB-1 was 97.6%. Its pK(a) was 5.73, which was very close to that of P227 and Cyanex 272. Its solubility in deionized water was 34.7 mg/L. Its extraction ability was equal to that of P227 and Cyanex 272. It can reach extraction equilibrium as fast as Cyanex 272. Its complex with Lu(III) has larger solubility in n-octane than that of Cyanex 272, which indicated that USTB-1 has higher extraction capacity than Cyanex 272. The Lu (III) loaded in USTB-1 solution can be stripped by HCI as easily as the Lu(III) loaded in P227 and Cyanex 272 solutions. USTB-1 has good separation performance for RE(III), especially for heavy RE(III). Its average separation factor of adjacent heavy RE(III) from Ho to Lu was 2.21, superior to Cyanex 272 root beta(N+1/N) from Ho to Lu: 2.08).