Clay suspensions are composed of anisotropic disk-like charged particles and are of great importance in many industrial applications because of their gelation. However, the origin of the gelation is still under debate. The synthetic hectorite-type clays such as Laponite XLG form clear dispersions due to their high purity and very small crystallite size, so that they are particularly suited to light scattering studies. In the present work, we reported the structure of Laponite XLG clay suspension and the gelation process by using both dynamic Light scattering (DLS) and small-angle X-ray scattering methods. The sol-gel transition (phase transition) was observed at a clay concentration of about 0.01 g/ml and the phase transition phenomena depends on neither the types nor the concentration of salt when below a certain salt concentration. Above a certain concentration of salt, flocculation (phase separation) was observed. The dependency of the value of this concentration on the salt type was the same as the empirical Schulze Hardy law for the critical coagulation concentration of isotropic colloidal suspensions. At low clay concentrations (below 0.01 g/ml), clay particles did not interact strongly; however, at higher concentrations (above 0.02 g/ml) where gelation and elasticity occurred, there were clear indications of interparticle interactions and random short-range ordering. DLS is thus one suitable method of analysis for the sol-gel transition without destroying the sample.