Cyclic hexapeptide 2, prepared from linear hexapeptide 1 of alternating d- and l-alpha-aminoxy acids, was found to adopt a C3 symmetric and bracelet-like conformation with consecutive eight-membered-ring hydrogen bonds (N-O turns) in nonpolar solvents, similar to that of valinomycin, a cyclodepsipeptide that binds cations selectively. However, 2 showed affinities for halide ions with selectivity following the order of Cl- > F- > Br-. The observed higher selectivity for Cl- (Ka = 11880 M-1) over F- (Ka = 30 M-1) in CD2Cl2 suggested that the selectivity of 2 for halide ions is mainly governed by the size complementarity rather than the hydrogen-bonding strength. Upon Cl- ion binding, the original bracelet-like conformation of 2 turned into a rather flat conformation with all six amide NHs pointing inward to form hydrogen bonds with Cl-.