Abstract: The non-covalent complexes of α-cyclodextrins and β-cyclodextrins (α-, β-CDs) with two aryl alkanol piperazine derivatives (Pipe I, Pipe II), were studied by electrospray ionization mass spectrometry (ESI-MS) and their dissociation constants (K_d) were also determined through static titration. The experimental results indicated that both Pipe I and Pipe II can conjugate to α-CD or β-CD and form 1:1 inclusion complexes. The K_d value obtained from ESI-MS coincided with those from the solubility studies. By comparison, it is concluded that the binding of CD-Pipe I is stronger than CD-Pipe II.