Abstract: The effects of the adsorption and surface micellization of dodecylpyridinium bromide(DPB) on the stability of silica(CAB-O-SIL) suspension have been investigated. The adsorption isotherms of DPB on a flame-hydrolyzed silica from aqueous solution exhibit two plateau(i.e.LS-type isotherm). In the presence of 0.1 mol/L NaBr the adsorption isotherm of DPB is displaced to lower equilibrium concentration region and the limiting adsorption is enhanced, but the adsorption in the first plateau remains nearly constant. In the low concentration range of DPB, the stability of silica suspension decreases with increasing concentration of DPB. However, near smc (surface micelle concentration) of DPB the stability increases sharply with increasing concentration of DPB. In the presence of NaBr, the stability of silica suspension is much lower in comparison with that without addcd salt. The results are explained in terms of the surface micellization model and the adsorption isotherms of DPB.