Abstract: Mass transfer kinetics of Eu(Ⅲ) extraction by hcptyl-1-methyl heptyl phosphonic acid(P5709) is investigated. Judging from the effects on mass transfer of stirring speed, interfacial area and operating temperature, the process of Eu(Ⅲ) extraction by P5709 is preliminarily considered to be diffusion-contr6lled. The effect on mass transfer process of pDlyamine type surfactant(Shang-205) is also studied. Experimental results indicate a sig-Continued on p. 163) nificant increase of resistance to interfacial mass transfer owing to the introduction of surfactant to the system.