Nowadays, high-durability has been required in concrete structures that assume long term-service. Therefore, generation of tobermorite in the concrete has been important for the material design of high durability concrete. The purpose of this research is to evaluate the effect of the addition of high volume CaO-MgO-SiO₂-based materials with autoclave curing for the generation of tobermorite, and to clarify the generation mechanism of tobermorite from the view point of the hydration reaction of materials at heating process in autoclave curing. As a result, generation of tobermorite was increased by using high volume CaO-MgO-SiO₂-based materials. It is because that C-S-H with high CaO/SiO 2 ratio was maintained, since the reaction of the α-quartz at heating process in autoclave curing was suppressed by substitution of CaO-MgO-SiO₂-based materials.Key words: CaO-MgO-SiO₂ based materials, Akermanite, Autoclave curing, Tobermorite, CaO/SiO 2 ratio , Silicate degree of polymerization, Development of (220)