A novel p-cyclodextrin derivative 4 bearing a pyridinio group on the primary side was synthesized by the reaction of 2-aminopyridine with 6-p-cyclodextrin monoaldehyde 3, and its complexation stability constants with several aliphatic amino acids have been determined in phosphate buffer solution ( pH = 7.2, 0.1 mol ?L^-1) at 25℃by using spectrofluorometric titrations. The stoichiometry is 1 : 1 for the inclusion complexation of amino acids with compound 4. Circular dichroism study indicates that the aromatic moiety was embedded shallowly into the cyclodextrin cavity. As a spectral probe, the pyridinio group in the modified cyclodextrin can recognize not only differences of the size and shape of amino acid molecules, but also the L/D-amino acid chiral iso-mer. As compared with mono-[6-（1-pyridinio）-6-deoxy]-p-cyclodextrin 5, compound 4 switched the enantiomer preference for L- to D-isomer, and showed the highest enantioselectivity of 5.4 for D/L-serine. These results are discussed from the viewpoints of ge