During 2003, about 980 thousand tons of waste plaster boards (WPBs) were released in Japan. An effective reuse of WPBs is a matter of social concern in Japan. This paper deals with the development of environment-conscious building materials (ECM-FSG) comprising pulverized waste plaster board (G), fly ash (F) and blast furnace slag (S). Authors intend to encourage the effective utilization of WPBs. Activators which accelerate the strength development of ECM-FSG at early ages are experimentally selected. Furthermore, methods for strength control of ECM-FSG are investigated. The results indicate that water to powder ratio is effective to control the strength of ECM-FSG paste and total pore volume plays a main role on the strength of the paste.