To activate the reactivity of sericite and make it have the abilities of ion exchange and intercalation between layers, the effects of heat treatment on crystal structure and reactivity of sericite were studied. The results, analyzed by XRD and Hall formula, indicate that sericite still retains its crystal characteristics after being activated by heat treatment at 500°C-800°C, but there are significant lattice distortions, and the maximum one occurred at 800°C. It can be seen from the SEM images that heat treatment reduces the order of sheets of sericite and makes the surfaces rough and the edges and corners smooth. The Al3+ dissolution amount from the sericite in HNO3 is 24.34 mg/g after heat treatment, which is increased significantly compared with the untreated one. It demonstrates that the reactivity of sericite is improved remarkably.