The paper deals with the monitoring of the structural changes of fine-grained cement-based composites in the early-age using acoustic emission method. After mixing, the cement-based materials exhibit continuous time-dependent structural changes which lead to the changes in the mechanical properties due to the chemical and physical processes. The events which are emitted due to the internal structure formation were detected using the acoustic emission techniques. A number of AE events are released due to the formation of new crystalline phases and due to microcracking in the material structure during the setting and hardening. The aim of the performed experiments was to extend the knowledge in the field of the early-age material characteristics and in the field of the internal structure formation of the cement-based materials. The results from temperature measurement show that mixture with microsilica has more slowly raised the internal temperature than mixture without microsilica. The results from acoustic emission measurement show that mixture with microsilica has lower activity of acoustic emission than mixture without microsilica during first six hours from measurement start.