Abstract: RELATIONSHIP BETWEEN SEPARATION FACTORS αANDαAND THE STABILITY CONSTANTS OF COMPLEXES WITH 2，6－PYRIDINE DICARBOXYLC ACIDYANG YUSHENG ；LI XIAOZHONG ；DING YUZHEN； LU JIACHUN（Northwest Institute of Nuclear Technology，P，O. BOX 69（17 ），Xi′an 710024）ABSTRACT The stability constants of the complexes of Am~93+)，Cm~(3+)，Pr~(3+) and Nd~(3+) with a number ofamino polycarboxylic acids are determined and collected and their various trends are comparedwith α-hydroxy carboxylic acids. It is pointed out that the separation factor of Am-Cmincreases with the separation factor of Pr-Nd． The semiempirical relationship of andis improved from for α-hydroxy carboxylic acids to for both α-hydroxy carboxylic acids and aminopoly carboxylic acids. According to this rela-tionship，2，6-pyridine dicarboxylic acid is selected for the determination of the stability constantsbecause of its high value in literature. The separation factor is as high as 1．99（acounted onβ_2）and the relationship between and thus has been verified further. Kev words Separation factors Stabilitv constant Amino polycarboxylic acids α-hydroxy carboxylic acid Am~(3+) Cm~(3+) pr~(3+) Nd~(3+)