[ $11AA$ ] tobermorite$(5CaO{cdot}6SiO_2{cdot}5H_2O)$ is synthesized from the mixtures of calcium hydroride and quartz using alumina in a molar ratio $Ca(OH)_2/SiO_2$ of 0.8 at $180^{circ}C$ for 8 and 24 hrs under saturated steam pressure. The influence of alumina on the formation of $11AA$ tobermorite was investigated by X-ray diffraction, differential thermal analysis and infrared spectroscopy. $11AA$ tobermorite containing increasingly larger amounts of aluminum showed a shift of the basal spacing from 11.3 to $11.6AA$. In general, there was a direct linear relation between the basal spacing and added content of alumina. The differential thermal analysis curves showed that $11AA$ tobermorite with increasing alumina contents exhibited the exothermic peak at high temperature, namely $11AA$ tobermorite containing aluminum gave a sharp exothermic peak at temperature around $850~860^{circ}C$ in the case of $S_3~S_5$. The absorption band at $1607~1620cm^{-1}$ is attributed to the bending vibration of water, and the position of the main O-H stretching and Si-O lattice vibration of $11AA$ tobermorite at 3500 and $965cm^{-1}$ respectively is not altered. Consequently the existence of alumina accelerates the crystallization of $11AA$ tobermorite, and that the aluminum ion appears to substitute for the silicon ion in $11AA$ tobermorite structure. Al-containing tobermorite is distinguished from Al-free tobermorite.