Abstract A method of measuring three-dimensional wave forms in a thin liquid film is presented, with experimental data. Water film thicknesses were measured instantaneously across the width direction by a newly developed multi-conductance probe, along nearly horizontal (4.1°) and near vertical (87.0°) flat plates with air - water concurrent stratified flow. The multi-conductance probe was composed of a large flush electrode and eleven wire electrodes, made of fine platinum wire of 0.05 mm diameter to minimize the flow disturbance. The measured data were processed to show the three-dimensional interface shapes, using wave celerity and computer graphics, and the reconstructed wave shape is compared with the real photographic image. The measuring technique is applicable for the shapes of both two and three-dimensional waves. The interfacial areas were also calculated from the measured three-dimensional wave shape. The increase in interfacial area is less than a few percent in a moderate range of the water film flow ( 500 < Re 1 < 1250 ).