The impact of mechanical activation on calcium hydroxide-based sorbent was investigated. Carbonation/decarbonation kinetics and sorbent cycle stability were characterized by in situ X-ray diffraction. By increasing the speed of ball milling, we could reduce the particle size and crystallite size while increasing the pore volume in the sorbent as evidenced by XRD, dynamic light scattering, and nitrogen physisorption. At 700 degrees C, mechanically activated (500 rpm planetary ball milled) sorbent showed a 24% increase in capture capacity over 10 isothermal carbonation-regeneration cycles when compared to the sorbent without mechanical activation. The possible reason behind this improvement is discussed, which links the microstructure evolution and sorbent regeneration rate.