Abstract: Following the selection of internals for a 109mm diameter fluidized bed, four kinds of internals were evaluated for a 360mm diameter fluidized bed on the basis of the oxidation of o-xylene to phthalic anhydride. The yield of phthalic anhydride was chosen as the test index. The results obtained were essentially the same as those for the previous smaller bed, i.e.,the lower baffles were the best, the perforated plate slightly inferior, and the vertical tubes the least ideal. But, when vertical tubes were used in combination with horizontal plates, equivalent effects were noted with plate-type baffles having smaller spacings. Regression equations showed that fluidized beds equipped with vertical tubes were less sensitive to temperature and gas velocity, implying that the flow patterns were not the same as those for horizontal internals.