In this study, the synthesis of lithium tetraborate in the presence of carbon dioxide (CO2) in an aqueous phase was investigated. A two-step process has been developed in the present study. The first step includes an aqueous phase reaction of lithium carbonate and boric acid in the presence of CO2 at different pressures. The second step involves the crystallization and thermal treating of the product obtained from step one at the temperatures between 300 and 400°C for 1 hour. Characterizations of the samples were performed by Fourier Transform Infrared Spectroscopy (FTIR), X-Ray Diffraction (XRD), Thermogravimetric Analysis (TGA) and Scanning Electron Microscopy (SEM). It was characterized that amorphous lithium tetraborate of Li2B4O7.3H2O was synthesized in the first step and then it was converted into Li2B4O7 in the second step. The use of CO2 as a modifying agent in lithium tetraborate synthesis has enhanced the dissolution rate of reactants that induced a fast-aqueous phase reaction.