It is known that application of non-thermal plasma to the surface of an aqueous solution has a potent effect in bacteria inactivation. From literature review, the low pH value has the most potent properties of bacteria inactivation. In this work, we investigate the influence of the voltage of non-thermal plasma generator on the pH of aqueous solution. Plasma treatment method is placed between two electrodes that are connected with an AC plasma generator. For this method, it is important to place the electrode at a specific orientation. The ground electrode is placed under the container that contains aqueous solution, making sure that there are no air gap. The power electrode is placed by a wire, dangling approximately 0.2cm above the centre of the test water. The resulting discharge is observed so that it appears between two electrodes and in the centre of the water. The water is treated for various high-voltage and time scale. In this method, the high-voltage is adjusted from 10,000 volt to 12,000 volt in order to measure the aqueous pH. The time scale is also measured for each voltage in order to gather precise data.