The leaching kinetics of niobium-bearing mineralisation in KOH hydrothermal system was investigated. Particle size analyzer, XRD and SEM were used for studying the influences of mechanical activation on particle size, surface area, crystal structure and surface morphology of niobium-bearing mineralisation. The results showed that mechanical activation decreased the mineral particle size, increased the surface area and the degree of lattice distortion or disorder. Kinetics of alkali leaching of niobium is modeled and explained. The activation energy of niobium leaching from unactivated niobium-bearing mineralisation was 45.6 kJ/mol. When the mineralisation was activated for 10 min and 30 min, the activation energy decreased to 32.2 kJ/mol and 21.9 kJ/mol respectively. Compared with the non-mechanical activation method, mechanical activation greatly improved the activity of niobium-bearing mineralisation and decreased the activation energy, so that the reaction speed was accelerated remarkably.