This article reports on the effect of liquid-state mechano-chemical activation on performance of nano-engineered cements (NEC). Microstructural characterization of NEC and contribution of activated cement (AC) phase were investigated using dynamic light scattering, X-ray diffraction, scanning electron microscope, and isothermal conduction calorimetry techniques. The effect of different parameters of liquid-state activation, such as duration of activation and the composition of the AC is reported. Due to intensive milling and hydration, the AC is composed of up to 25% of nano- and submicrometer- sized cement grains and products of hydration, mainly, C-S-H and ettringite. Different quantities of AC (at 10%-30% cement replacing levels) were tested in NEC mortars. The compressive strength of NEC based materials with different types and dosages of AC was investigated. Research results demonstrated that proposed top-down approach for production of nano-sized and submicrometer phases of AC acting as seeds increases the rate of cement hydration and improves the compressive strength of cement-based composites.