A model is developed to predict bed voidage in liquid-solid fluidised bed based on slip velocity concept. The model considers comprehensively all hindrance effects such as wall effect, buoyancy effect and particle-particle effects. Experimental data on bed expansion, pressure drop and bed voidage are collected in a column of 7.53 cm i and 100 cm in height, covering a wide range in now rate of the fluid and physical property of materials. The model predictions are satisfactorily compared with the experimental data of the present study as well as that reported in literature.