Abstarct: Currently, adjusting pH of waste water by using lime, sodium carbonat and coloridric acid. Unfortunatly, these materials entrance to the environment as pollution and have disadvantages for environment. Present study aimed to adjust the pH of an aqueous solution by micro/nanobubbles (MNB) of pure CO2 (P. CO2) and CO2 of burning methane (B. CO2) as well as O3, O2, and air in a continuous system. In this research, samples with alkalinity pH prepared by aqueous 2M of KOH, NaOH and saturated solution Ca(OH)2 followed by reduction of the pH by injecting MNB of P. CO2 and B. CO2. In the next step, simultaneous injection of MNB to alkaline aqueous 2 molars of KOH, NaOH and saturated solution Ca(OH)2 with MNB P. CO2 and B. CO2 was studied. Furthermore, in some experimental at first, pH was decreased by MNB P. CO2 and B. CO2 and then increased it by injecting 2 M solution of KOH, NaOH and saturated solution Ca(OH)2. At the end, pH increased by adding MNB of O3, O2, and air into the water.The type and volume of alkaline and acid used, time, and initial pH were effective parameters in this research. According to the results, MNB P. CO2 could decrease solutions’ pH more than other MNB and could fix pH after 120 seconds. The highest pH achieved by MNB of O3 and O2.