2-amino-5-(4-fluorophenyl)-1,3, 4-oxadiazole (1) is a compound of ambident reactivity. Its solid-state acetylation by acetyl bromide vapours results in two monoacetyl derivatives and two diacetyl derivatives. Their structures were confirmed by UV spectra, mass spectra and thin layer chromatography data. The solid-state acetylation of compound (1) is an anisotropic reaction and the different products are formed on different crystal facets : amino-derivatives-on (110) and(<(11)over bar 0> crystal facets; imino-derivatives-on (001) facets. The crystal facets’ reactivity is determined by the reactive centres of molecules that break out on the reaction surface. X-ray analysis shows that molecules of the reagent diffuse into channels in aminooxadiazole crystal. There the channels are perpendicular to to the plane of crystal facets; their diameter is about 8 Angstrom.