The density of bentonite and of bentonite-sand mixture is the prime criterion in the evaluation of the swelling pressure and deformation of buffer material which must be taken into consideration in the design of any type of waste disposal facilities. A series of laboratory swelling pressure and deformation tests using variable dry density of the specimens has been carried out to investigate the characteristics of buffer material for radioactive waste disposal. Initial dry density and loading pressure on the specimens has a noticeable influence on maximum swelling rate. Temperature is also an important factor in the control of the swelling rate of compacted bentonite. The void ratio increased in high initial dry density material and decreased for low level initial dry density when compared with the initial state at the end of swelling due to static load. The swelling pressure fluctuated with elapsed time in respect to temperature. The maximum swelling pressure is dependent on the initial dry density and the content of bentonite in bentonite-sand mixture.