The Al-substituted 11Å tobermorite was synthesized from aegirine-augite syenite potash ores by alkaline hydrothermal reaction at 300°C. The obtained tobermorite was characterized by chemical analysis, X-ray diffraction and scanning electron microscopy. The effect of reaction time on the tobermorite formation and the dissolution ratio of the K2O in the potash ores were investigated. It was revealed that the dislocation ratio of K2O increases with increasing reaction time. The main rock constituents were converted into a well-crystallized Al-substituted 11Å tobermorite after 3 hours hydrothermal reaction at 300°C. The obtained Al-substituted tobermorite forms hollow spherical aggregates with the diameter of 40µm-80µm by the crossing of fibrous tobermorite crystal together. The Al3+ may substitute isomorphously up to 15 at % of Si 4+ in the obtained tobermorite.