A layered alkali silicate, octosilicate (Na2Si8O17 center dot nH(2)O), was functionalized ith sulfonic acid to impart swelling ability in water. To immobilize the sulfonic acid group on octosilicate, (3-mercaptopropyl)trimethoxysilane was attached in the interlayer space and subsequently oxidized. Surface coverage with the sulfonic acid group (0.7, 1.3, and 1.7 groups per Si8O17) was controlled by changing the added amount of the silane coupling reagent (0.7, 1.3, and 2.0 groups per Si8O17). The sulfonated octosilicates hydrated to expand the interlayer space, where the degree of expansion varied with the surface coverage of sulfonic acid. For the sulfonated octosilicate with the lowest surface coverage (0.7 group per Si8O17), the remaining interlayer silanol group was efficiently grafted with the trimethylsilyl group to expand the interlayer space further upon hydration. The effect of the electrolyte concentration on the hydration of the sulfonated octosilicates was investigated to find that with the increase in NaCl concentration the basal spacing decreased. The sulfonated and trimethylsilylated octosilicates were dispersed in water to form colloidal suspensions with varied transparency.