Abstract: In this paper, the extraction of lanthanides and yttrium with CHC13 solution of 4,4'-decanedioyl-bis-(1-phenyl-3-methyl-5-pyrazolone) (DBPMP) is studied. The ionic strength ot the aqueous solution is controlled at 0.1 with sodium perchlorate. All the rare earth elements are extracted as MA(HA) . The equilibrium constants, pH1/2 (5.0×10-3mol/l D3PMP-CHC13)and the separation factors for each pair of the rare earth elements are calculated and compared with those of PMBP. The results show that DBPMP possesses much higher extractin and separating capability than PMBP. Especially, the separation factor for La-Ce is as high as 2.04×102 and the average separation factor from La to Tb is 3.84 Results of the thermodynamic studies of extraction about Ce, Pm, Tm and Lu are also reported.