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The amount of fly ash disposed as industrial wastes is increasing with increasing coal demands all over the world. Although fly ash is generally disposed by landfill, the demand of effective utilization of them is increasing because of the limitation of the disposal site. 80 % of coal ash is utilized such as a material for cements though less of them are disposed by landfill. Considering the preparation of landfill area and environmental issues, it is very meaningful to discuss the utilization of fly ash except a cement usage. Most of coal is mined by open-pit mining method in Indonesia. A broad post-mining area is built after the mining operation. The broad area has to be revegetated in terms of environmental conservation. However, soil acidification caused by mixing acid sulfate rocks or soils mined in the operation influences the revegetation. As the plant growth is inhibited under the acidic conditions, the utilization of fly ash which has higher neutralizing capacity due to its alkalinity is expected in order to improve the conditions of seedbed in the revegetation area. In this paper, the utilization of fly ash for preparation of seedbed in disturbed land in Indonesian open cut coal mine is discussed by means of laboratory vegetation test by using simulated acidic soil with a mixture of pyrite, fly ash which has higher alkalinity, and Acacia mangium which is a typical species planted for fast growing tree in Indonesia. The results suggested that the appropriate mixture of fly ash to neutralize the acidic soil can be improved the plant growth under the acidic condition.