A molecular dynamics simulation of a gamma-Al2O3 microcrystal has been performed in order to investigate the structure of both the surface and the bulk. Ou results show that an approximately cubic particle of 60 Angstrom per side has a crystalline inner structure and an amorphous phase which constitutes the proper surface with a depth of about 12 Angstrom. Some structural properties of this important catalytic support are analyzed and confirm both results from previous simulations on the surface and the bulk and from experimental investigations by other authors. The nature of Lewis acid sites is also considered and compared with recent studies based on Al-27 CP-MAS and IR spectroscopy.