Abstract: Viscosity properties of silica sol with different concentrations were investigated.Effects of adding different surfactants into silica sol on its viscosity properties were studied by means of viscosity method.It was found that direct addition of three surfactants all resulted in reduction of viscosity in various degree,of which sodium dodecylbenzenesul fonate （SDBS） is more effective than emulsifier OP-10 and sodium dodecyl sulfate （SDS）.It was speculated that the mechanism of viscosity reduction relied on the covering process of SDBS on the colloidal particles.Effect of concentration on the viscosity reduction of SDBS behaved as critical micelle concentration rule, and critical concentration was about 4.6×104.6 ×10<SUP>-3</SUP>mol/L.