Zeoliles were synthesized from fly ash by alkaline hydrothermal activation. Fly ash from the power plant in Mae-Moh was the starting material. The variables studied were; type of base solution (NaOH and KOH), concentration (1.0, 2.0, 3.0 and 4.0 M), temperature (70, 100 and 120 ํC), reaction time (24, 48, 72, 96 and 120 hr) and sample concentration of 0.125 g/mL The reactor for activation consists of oil bath and mechanical stirrer which stirring all time in the experiment. Powder patterns of X-ray diffraction analysis have shown that several types of zeolite such as zeolite P, chabazite, nepheline and gismondine were successfully synthesized under certain experimental conditions. Other compound identified were Sillimanite, Willhendersonite, Gehlenite. The optimum condition for activation were found to be; in case of activation by NaOH solution; concentration of 2.0 molar, 100 ํC and 72 hr. If activation by KOH solution; concentration of 2.0 molar, 100 ํC and 72 hr. Zeolites synthesized at the optimum condition had cation exchange capacities 619.44 mmol/kg. But cation exchange capacities was 52.20 mmol/kg for fly ash
