pH responsive porous glass of which pore radius was ca. 4 nm was successfully obtained by its surface modification with COOH group on its pore surface. Surface modification with COOH group was performed by the hydrolysis of CN group on its pore surface. Its response speed of acetone in 3 mol/L aqueous solution under acidic condition (pH = 2.8) was twice as large as that under basic condition (pH = 10.8). This was caused by COOH group state on its pore surface with pH. It shrinks under acidic condition, whereas expands under basic condition as if the gate of pore of the porous glass opened and closed with changing pH. The amount of COOH group on its pore surface was approximately 2.5 mu mol/m(2). (C) 2013 Elsevier Ltd. All rights reserved.