This paper presents an experimental study on the effects of elevated pressure and particle size distribution (PSD) on the minimum fluidization velocity (U-mf) and the bed expansion. It was developed with Geldart B and D-type polystyrene particles. Four wide PSDs and five narrow PSDs were investigated. The four wide PSDs studied included a Gaussian distribution, a flat distribution, a ternary mixture, and a binary mixture, all with the same mean diameters. Operation pressure ranged from 0.1 MPa (absolute pressure) to 2.7 MPa. The results revealed that the U(mf)s of the wide PSDs were lower than that of the reference narrow PSD with the same diameter at pressures exceeding 0.3 MPa. The segregation tendency of wide PSDs decreases with the increase in the operating pressure. The four wide PSDs had obviously different U(mf)s at pressures below 0.9 MPa; however, this difference in the Units was gradually reducing with a further increase in the pressure (>0.9 MPa). The bed expansion increased with increasing the pressure at same excess fluidized gas velocity. Correlations basing on experimental data were proposed in order to predict the U-mf and bed expansion for the narrow PSD at elevated pressures, and three correlations were investigated for predicting the U-mf of wide PSD. (C) 2017 Elsevier B.V. All rights reserved.