Silica sol was used for the first time to stabilize sodium dodecylsulfate (SDS) foams in order to avoid aggregation of nanoparticles in aqueous solutions. The stabilities and rheological properties of SDS foams stabilized by silica sol and silica nanoparticles were characterized using a Waring blender, an R/S plus rheometer, and an extensional viscoelasticity meter in order to illustrate the better performance of the former. The results showed that the foam stability (liquid drainage half-life) increased by 29.3% and 21.1% after addition of 0.05 wt% silica sol and silica nanoparticles, respectively. The rheological properties of foams with added silica sol were the best, followed by those with added silica nanoparticles and those without additives. Both the viscosity and elasticity of the liquid film were increased better after addition of silica sol rather than silica nanoparticles. The better dispersity of silica sol may have been the main reason for these results.