The phosphoric acid-based metakaolinite geopolymeric materials with different SiO2/Al2O3 molar ratios were prepared from metakaolinite, Al2O3 powder and phosphoric acid. X-ray diffraction (XRD), Thermogravimetry and Differential Scanning Calorimeter (TG-DSC), Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM) were used to determine the reaction process and phase formation. The results indicated that different SiO2/Al2O3 ratios raw materials can generate geopolymers composition of the amorphous phase and quartz crystalline phase. The still existed quartz peaks indicate that quartz from metakaolinite did not totally take part in the chemical reaction or dissolve into the gel phase of geopolymers. The best performance was observed in the geopolymeric material prepared with SiO2/Al2O3 molar ratio of 1.4 due to the proper obtained Si-O-Al-O-P-O-bonds in geopolymeric structures. The acid-based geopolymers were stable below 1450 °C. These geopolymers have a potential use in fireproofing materials, since they display important high temperature stability.