Geopolymers made from metakaolin and an alkali solution were immersed in a 0.1 mol/L copper chloride solution for 24 h. After the solution treatment, the surface color of the geopolymers changed to green to a depth of 900 mu m due to ion exchange with copper ions. To evaluate the antimicrobial activity of the colored portion of the geopolymer, it was ground into 500 mu m particles and mixed with a 10:1 mass ratio of oyster mushroom (a wood-rot fungus) and sawtooth oak sawdust. This mixture was placed in a glass bottle at room temperature and 100% relative humidity for one week. The results revealed that the geopolymer ion-exchanged with copper ions suppressed the growth of oyster mushrooms in sawtooth oak sawdust, indicating antimicrobial activity. (C) 2015 Elsevier Ltd and Techna Group S.r.l. All rights reserved.