Porous polyurea films were synthesized by vapor deposition polymerization via ionic liquid (IL) nano thin films with different thicknesses, and the water contact angles (WCAs) on the polyurea films were measured. The promotion of polymerization and its accompanying porous structural formation became detectable for IL thicknesses above similar to 20 nm. The WCA tended to increase with an increase of surface roughness of the porous polyurea films. The mechanism of such IL-assisted polymerization and porous structural formation will be discussed.