The influence of syneresis on the shear strength parameters of both sodium silicate-formamide and sodium silicate-glyoxal grouted sands was investigated under wet-cured as well as air-dried conditions. Syneresis of sodium silicate-formamide and sodium silicate-glyoxal grout gels increased with the increase of sodium silicate content up to a certain point. After which, as the silicate content of both grout gels increased, their syneresis decreased. In general, syneresis of sodium silicate-glyoxal grout gels was higher than those of sodium silicate-formamide grout gels. Syneresis of sands injected by the above-mentioned grouts was also observed and found to be less compared to the related grout gels. Triaxial tests were run on both wet-cured and air-dried sand specimens at different time intervals to determine the effect of syneresis on the internal friction angle and cohesion intercept of grouted sands. Due to syneresis, the shear strength parameters of wet-cured sand specimens decreased with time to some extent and then ceased to have an effect. In contrast, the shear strength parameters of air-dried sand specimens increased with time up to a certain point, even though they underwent syneresis, and then became stable.