In order to decrease the grain size of Al 2 O 3 coatings deposited from the usual AlCl 3 /CO 3 /H 2 reaction gas mixture, Al-acetylacetonate (Al-acac) was added in the concentrations of 1000, 10 000 and 50 000 mol-ppm (relative to mol AlCl 3 ). TiC-coated cemented carbide substrates were used.Extremely fine-grained Al 2 O 3 coatings were obtained by adding 50 000 mol-ppm Al-acac. At a total pressure of 50 torr this grain refining effect of Al-acac is restricted to the first two substrates (10 mm). A decrease in the total pressure, from 50 to 5 torr, and therefore a decrease of the time the reactants spend in the reaction chamber, increased the grain refining influence of Al-acac up to four substrates (20 mm).The Al 2 O 3 growth rate itself was not influenced by the different Al-acac additions.