Cyclodextrins (CD) form inclusion complexes with different guests owing to the fact that the shape of the CD molecule is a truncated cone with a hydrophobic cavity. The adducts of CD with metal complexes remain scantily explored. In this study, the stability constants of the adducts between succinate copper(II) complexes and -CD was determined using capillary electrophoresis. The -CD concentration in background electrolytes (BGE) was found to influence on the effective electrophoretic mobility of the copper(II) complexes in succinate BGEs. It was shown that succinic acid and its anions and copper(II) ions did not form a significant amount of the inclusion complexes with -CD and the mobility change was caused by the adduct formation between succinate copper(II) complexes and -CD. The stability constants of these adducts were determined at 25 degrees C and ionic strength of 0.100M: log (CuL22-/-CD)=1.76 +/- 0.06, log (CuL0/-CD)=0.98 +/- 0.09. The [CuHL](+) and [CuHL2](-) species were found to do not form adducts with -CD.