The rate of removal of a thin film of organic impurities during discharge cleaning in pure oxygen plasma was studied. Aluminum discs with a thickness of 2mm and a diameter of 18mm were first cleaned and then covered with a thin film of a polymer. The thickness of the film was estimated by AES depth profiling and was found to be about 36nm. The samples were exposed to oxygen plasma. The plasma density and the electron temperature were measured with a double Langmuir probe and were about 1x10 1 6 m - 3 and 6eV, respectively. The density of neutral oxygen atoms was measured with a catalytic probe and was 3.2x10 2 1 m - 3 . Samples were exposed to the oxygen plasma in 5s pulses in order to prevent their heating. The total treatment time was between 10 and 50s. After plasma treatment the samples were analyzed with AES. The depth profiles showed that the thickness of the carbon layer on the surface linearly decreased with plasma exposure time. The slope of the line was about 0.8nm/s. Taking into account the known flux of O atoms on the sample surface enabled an estimation of the probability for oxygen atoms to react with carbon on the surface. The calculated probability was about 1x10 - 4 .