The present paper reported the hydration kinetics of high-strength concrete with untreated coal bottom ash to further understand the mechanism of internal curing with bottom ash. As a reference material, a type of commercialized artificial lightweight aggregate was used. Prior to investigating the hydration of concrete, the microstructure of the concrete was observed by using a backscattered electron (BSE) type scanning electron microscope. To systematically investigate the hydration kinetics of the concrete, the degree of hydration was measured and a thermogravimetric analysis (DTA/TGA) for cement mortar was conducted. In addition, the relationship between the hydration kinetics and mechanical properties of concrete containing both types of aggregates were analyzed. It was found that the tendency of hydration enhancement by bottom ash was affected by 1) the escape of water from bottom ash into the cement paste before setting of the fresh mixture, and 2) the high pozzolanic reactivity of bottom ash.