A numerical study on mixing/segregation phenomena in a pressurized fluidized bed with large particles of Geldart D type of binary density but same diameter with high velocity gas was performed by the use of discrete particle simulation. Particle mixtures are composed of spherical particles with 2 mm diameter and 1 g/cm(3) flotsam density and different jetsam densities of 1.25, 2 and 2.5 g/cm(3) with jetsam volume fraction of 0.5. The particles are initially packed approaching perfect mixing state in a rectangular bed and then fluidized by gas uniformly injected at the bottom of the bed. Effect of increase of pressure and density ratio was investigated and mixing/segregation behavior is discussed in terms of flow patterns, solid concentration profile, height variation, pressure drop variation and mixing kinetics. The results show that increase of pressure causes a more vigorous and chaotic motion with more slugs and large bubbles. With increase of pressure, pressure drop and height of the bed increase and both of them fluctuate more with larger amplitude and shorter frequency. Mixing index also decreases with the increase of pressure, and thus solids' mixing diminishes. Effect of increase of density ratio is somehow like effect of increase of pressure in most cases but has a little difference in some cases. (C) 2013 Elsevier B.V. All rights reserved.