The preparation of 4-bromophthalic anhydride is described. This compound, useful as raw material for production of dianhydride monomers such as bisphthalic dianhydride, oxy-bisphthalic dianhydride and several bisphenol dianhydrides for the specialty polyimide sector, was prepared via gas phase oxidation of 4-bromo-ortho-xylene with air over a V-Ti-P catalyst in a yield of 85%. Oxidation of 3-bromo-ortho-xylene gave only a 45% yield of 3-bromophthalic anhydride. Mixtures of 4- and 3-bromo-ortho-xylene gave, as expected, mixtures of 4- and 3-bromophthalic anhydride which were enriched in the 4-isomer (in comparison with the starting bromoxylene isomeric composition).