Nano-porous silica aerogel monolithics were prepared by sol-gel process from methyltrimethoxysilane (MTMS) precursor through drying under ambient pressure and temperature, and the densities of the aerogels were between 0.16-0.33 g/cm3. The resulting aerogels were characterized by means of FT-IR, SEM, TG and BET. The results show that when keep the molar ratio of MTMS:MeOH:H2O constant, the change of the concentration of ammonia has distinct effect on the properties of silica aerogels, such as gelation time, bulk density, volume shrinkage and monolithicity.