The influence of a single microstructure on liquid-side controlled mass transfer is studied for liquid film flow over an inclined plate with a film height of less than 1 mm. Planar Laser Induced Fluorescence (PLIF) is adapted and used to measure oxygen absorption at three gas flow rates. The liquid is a mixture of water, ethanol and glycerol. A ruthenium complex is used as a fluorescence indicator. By combining PLIF with dynamic fluorescence quenching, local concentration fields are visualized and determined through image processing. The results show that the local mass transfer coefficient decreases in the flow direction on a smooth inclined plate. Compared to a completely smooth surface, the local mass transfer tends to be enhanced in the direct vicinity of a single microstructure. The impact of the microstructure on local mass transfer depends on the gas flow conditions and the measurement position. The highest local mass transfer coefficients are measured, where the local film thickness is lowered due to the structure and with lower gas flow rates. (C) 2019 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.