Water glass adhesives based on sodium silicates have been modified by addition of phosphorous or boron. In the preparation of sodium silicate, mixtures of silica sand and sodium carbonate with the additives was melted at 1400degreesC. They were dissolved in an autoclave at 180degreesC, and then concentrated to have a final viscosity for the comparison of their adhesive property and water resistance with the conventional liquid sodium silicates without additives in SiO2/Na2O molar ratio 2.5similar to4.2. Obvious increase of the water resistance was observed for the liquid sodium silicate samples with the 5% P2O5 or B2O3 additives in the solid contents without loosing its adhesive property.