Water swelling behaviors of silica-filled NBR composites in deionized water and NaCl solution were investigated by changing the swelling medium. Variation of the water swelling behaviors with the silica content was also investigated. The water swelling ratios increased with increasing the silica content. The water swelling ratios in deionized water were higher than those in NaCl solution. By changing the swelling medium from the deionized water to the salt solution, the water swelling ratio decreased or slightly increased at the point of swellingmedium change. For the swellingmedium change from the salt solution to the deionized water, the water swelling ratio notably increased when the swelling medium was changed. Low water swelling ratio in the salt solution was explained with the hydrated ions and ionic atmospheres.