The laser light scattering microscopy under the total internal reflection condition allowed one to do in situ measurements of individual W/O microemulsions of aerosol OT (AOT) formed spontaneously at a dodecane/water interface in a thin-layer two-phase microcell. The instrument can detect the AOT microemulsions being larger than 50 nm in hydrodynamic radius at the interface and in the dodecane phase without any probe molecules.