Osmotic dehydration experiments of "difficult-to-filter" bentonite slurry were conducted with the aid of the high osmotic pressure brought about by hypertonic solution. In the experiments, osmotic dehydration was conducted by submerging a dialysis membrane tube containing bentonite slurry in polyethylene glycol solution. It was found that this method is quite effective for dehydration of "difficult-to-filter" slurry. It was clarified that the dehydration behaviors can be analyzed separately divided into two parts; filtration and subsequent consolidation. In the filtration period, the dehydration behaviors were well described by the Ruth filtration rate equation, in consideration of the compressibility of the filter cake. Also, the dynamic behaviors of dehydration in the consolidation period were accurately described by the modified Terzaghi model. The variations over time of the mass of the bentonite slurry during osmotic dehydration were well evaluated using in combination with the Ruth filtration rate equation and the modified Terzaghi model.