Recently in Japan, some chemical expansive materials have a tendency to be used for demolition of rock-like materials, old concrete structures etc. Those are called as “expansive demolition agent”. With the agent. demolition work can be done in safety without sound. vibration and any other pollution. since high expansive pressure is obtained gradually by only mixing the agents with water and pouring the sully into bored holes. In order to estimate the time for demolition works, it is necessary to clarify the amount of the expansive pressure acting on the inner surface of the holes and mechanism of fracture of materials demolished. The authorsi carried out experimental and theoretical studies to clarify the above problems, and give how to design the demolition works with the agent.