The invention relates to a method for producing phthalic anhydride by means of catalytic vapor-phase oxidation of o-xylol/naphthalene mixtures with molecular oxygen while using a catalyst (I) situated in a first layer on the gas entry side, said layer amounting to 25 to 75 percentage by volume of the total catalyst volume, containing, each time with regard to the catalytically effective mass, 1 to 10 wt.% vanadium oxide (calculated as V2O5), 1 to 10 wt.% antimony oxide (calculated as Sb2O3) and 80 to 98 wt.% titanium dioxide of the anatase type with a BET surface of 13 to 28 m2/g, and 0.05 to 1 wt.% cesium (calculated as Cs), deposited on a steatite support. In addition, the phthalic anhydride is produced by using a catalyst (II) situated in a second layer, said layer amounting to the remaining 75 to 25 percent by volume of the total catalyst volume, containing, each time with regard to the catalytically effective mass, 1 to 10 wt.% vanadium oxide (calculated as V¿2?O5), 1 to 10 wt.% antimony oxide (calculated as Sb2O3) and 80 to 98 wt.% titanium dioxide of the anatase type with a BET surface of 13 to 28 m?2¿/g, 0.01 to 1 wt.% phosphorous oxide (calculated as P) and 0.01 to 0.2 wt.% cesium (calculated as Cs), deposited on a steatite support. The cesium content of catalyst (II) is less than 15 wt.% of the cesium content of catalyst (I), and catalyst (I) and catalyst (II) are produced without adding compounds of niobium.