Self-assembled monolayers of thioether substituted subphthalocyanine [BClSubpc(S<i>n</i>-C<sub>12</sub>H<sub>25</sub>)<sub>6</sub>] were prepared by deposition from solution. The adsorption kinetics of the molecules on gold substrates was characterized in situ and in real time by optical second harmonic generation (SHG). The obtained data have been fitted with three standard kinetic models and best agreement has been found using the first order Langmuir kinetic model. Subsequently, ellipsometry measurements have been performed to determine the thickness of the formed molecular layers. The extracted thickness was 13.0 nm, demonstrating the formation of a monolayer.