Metakaolin (MK) is a material used in the construction field, mainly as pozzolanic additive for modern cement and concrete. MK mainly consists of silica and alumina oxides, with variable contents of other oxides that can be considered as impurities. With the aim of overcoming the drawback represented by the non-homogeneous properties of natural MK due to significant variability of its structure, chemical composition and reactivity, four pure aluminosilicates with formula Al2O3•2SiO2 were synthesized and characterized in the present study. Aluminosilicate gels were synthesized by the sol-gel method using ANN and TEOS as precursors of Al2O3 and SiO2 respectively. Both precursors were dissolved in pure ethanol. Several samples were obtained with four different TEOS/H2O molar ratios. Before the thermal pre-treatment of the gel materials their thermal behaviour were analysed by thermal analysis with the aim to choose the most suitable temperatures. The sols were dried at 65°C for 24 hours, and then at 120° for 1 h. Since the results showed that dehydroxylation (which leads to the conversion of Al(VI) into the more reactive Al(V)) begin to occur at around 500 °C [1], the samples were subsequently heated up to 600°C in order to induce dehydroxylation. The FTIR spectra of all the synthesized samples after heating at 600°C compared to that of MK were found very similar to each other. Therefore, FTIR analysis showed that a higher amount of reactive Al(V) is present in the synthesized material compared to natural MK. Furthermore, no impurities were detected in the sol-gel powders whereas impurities are present in the natural MK, though in small amount. The colour of the powders confirms the result of the XRF analysis: MK is grey, whereas all the sol-gel powders are white. The XRD spectra of all the calcined samples and of the fresh MK revealed that they are completely amorphous, and SEM analysis confirmed that all the samples are homogeneous and compact, regardless of the water content. Finally, ICP analysis shows that the synthesized aluminosilicates release a higher amount of Al and Si than natural MK, regardless the TEOS/H2O molar ratio. These results suggest that the synthetic materials are more reactive than ‘natural’ MK and can be suitably used as raw materials, as a MK substitute.