Porous silica low-k films have been prepared from coating solutions containing noncrystalline silica nanoparticles and polysorbate surfactants (Tween 20, Tween 40, or Tween 60) with different hydrophobic tail lengths, in which the critical micelle concentration (CMC) and the hydrophilic property of the surfactants both decrease with increasing tail length. It has been found that more pore volume can be generated in the samples by using surfactant with longer tail length, because of the formation of more micelles in coating solutions. However, only the film prepared with the shortest tail length (i.e., in Tween 20) can possess an ultra-low-k value below 2. A stronger interaction between silica nanoparticles and the surfactant with shorter tail length has been detected. The presence of residual silanol groups within the films after a hexamethyldisilazane (HMDS) treatment can be decreased substantially by decreasing surfactant tail length. It has been concluded that the less remaining of silanol groups can cause the film to possess lower k values, lower leakage current densities, and higher breakdown fields. By using solid-state 29Si NMR, thermal analyzes and FTIR for characterization, the effects of different tail lengths on silanol groups during the preparation of coating solutions and coated films have been explored.