Formation of artificial opal films by a vertical deposition method was in situ studied using the grazing incidence X–ray diffraction technique. Monodisperse spherical polymethyl methacrylate particles (200 nm in diameter) were deposited on the polished Si substrate from an aqueous suspension. The ordering of particles on a fixed area of the substrate located in turn in the bulk suspension under the meniscus and in the air was continuously monitored by the Xray scattering upon moving the meniscus down owing to evaporation of the solvent. The triple air–liquid–solid phase boundary, i.e. the top line of the meniscus, is identified as the most probable location of the crystallization process. The analysis of observed Bragg reflections and the particle formfactor indicates that the obtained artificial opallike structures are composed of the spheres arranged in a closepacked hexagonal layers parallel to the substrate. The characteristic correlation length along the normal to the substrate of 550 ± 100 nm is obtained from the half full width of Bragg peaks.