Association constants of complexes of a new class of cyclodextrin alkyl derivatives - randomly susbstituted tert-butyl derivatives (TB-CDs) with complete set of mono-halobenzoic acids and acridine derivatives were measured using capillary electrophoresis and compared with association constants of natural cyclodextrins. In most cases the association constants of natural cyclodextrin and its corresponding tert-butyl derivative were comparable. Strong dependence of association constants on actual cyclodextrin concentration was observed for complexes of tert-butyl-α-cyclodextrin with acridine derivatives. Significant increase of the association constant occurred below the critical micelle concentration of the cyclodextrin derivative, while an increase above this value was less significant.