The hydraulic behavior of synthetic merwinite was investigated after activation by two different methods, aiming to enhance its hydraulic activity which is weak in water. Mechanical activation, by means of extensive milling in a bead mill, led to amorphization of merwinite and a decrease in its crystallite size. The combined effect of higher specific surface area and of structural disorder resulted in a notable increase of hydraulic reactivity. The hydraulic reactivity was substantially more pronounced with chemical activation compared to mechanical activation. Crystalline and amorphous C-S-H and brucite were the main hydration products formed in the hydrated, mechanically activated merwinite, whereas portlandite precipitated additionally in the case of chemical activation. Spectroscopic analyses of FTIR and Si-29 MAS NMR verified the C-S-H formation. TEM investigations revealed formation of Mg-low C-S-H gel around the merwinite particles. Both mechanically and chemically activated merwinite systems were capable of developing mechanical strength.