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Summary form only given. Although cold atmospheric plasmas show a high killing/inactivation rate for the bacterial samples seeded on agar, the ex vivo porcine skin model as well as the in vivo test on human skin give obviously decreased inactivation rates due to complex structure of the target surface. In addition, the aqueous medium can protect the bacterial substance from the direct exposure to the plasma generated reactive species. So that much slower bactericidal efficiency is normally found for the plasma treatment in solutions. Using the surface micro-discharge (SMD) plasma, previous results have shown that, about 5 log <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">10</sub> steps of the bacterial load can be achieved in some seconds when the bacterial sample is prepared on agar with a dry surface condition <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sup> , however it takes around 10 minutes to obtain 5 steps of log <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">10</sub> reduction on ex-vivo porcine skin model even with a sufficiently drying surface <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> , and 1-2 log <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">10</sub> steps was observed within 30 seconds for the in vivo test on human lower-arm skin <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> . In this contribution, we will show the effect of the aqueous medium on the bactericidal effect of the SMD plasma. Different mediums with different bacteria concentration were distributed to agar plate to produce a thin layer of bacterial solution with a thickness in the range of 50 μm to 300 μm. The prepared samples were then immediately applied the plasma treatment. The survival curve of the bacteria with respect to different plasma treatment time was obtained. In addition, the chemical species generated by the SMD plasma were measured by a mass spectroscopy with considering the effect of the aqueous surface for the plasma treatment.