The effect of atomically dispersed phosphorus on Mo2C- and WC-supported gamma -Al2O3 has been studied. Phosphorus was introduced via molybdenum or tungsten heteropolyanions. Mo- and W-based heteropolyanions were used to synthesize supported materials. Propene and tetralin hydrogenation were used as molecular probe reactions to test the activity and selectivity of the alumina-supported molybdenum or tungsten carbides. The effect of phosphorus on the hydrogenation activity of materials was also considered. Catalysts were characterized by X-ray diffraction, transmission electron microscopy (TEM), energy-dispersive spectroscopy (EDS) and CO chemisorption. Phosphorus was found to increase significantly the activity of molybdenum and tungsten carbides. Supported molybdenum carbides are highly dispersed. Tungsten carbide particles are well dispersed with sizes ranging from 2 to 4 nm. To check the stability of carbides they were characterized after catalytic runs.