We have carried out magnetization measurements of a single decagonal Al72Ni
12CO16 quasi-crystal for the cases of the magnetic field parallel and perpe
ndicular to the periodic axis with a torsion-type magnetic balance in vario
us magnetic fields up to 10 kOe from 4.2 K to room temperature. Anisotropic
diamagnetic susceptibility was observed, which is closely correlated to th
e electron motions in the quasi-crystal.