In this paper the mineralogy and geochemistry of selected Greek and Chinese coal fly ash are examined. Coal is the main source of energy in China and Greek energy system. China is one of the main coal-burning countries, while in Greece lignite has a share of 75% in the electricity production. The production of fly ash in China was around 100 million tones in 2002 while in Greece lignite fly ash accounts around 10 Mt. Even though the mineralogical and chemical composition of the fly ashes coming from these two countries differs, there are common questions on the utilization of this material. The Variation of the Greek fly ash chemical composition, from Ca-poor to Ca-rich, fly ash, has resulted to Applications such as dam construction. Use in cement and possibly in concrete and road construction. On the other side Chinese fly ash, which is rich in mullite, is broadly applied for brick making. The production of zeolite from Greek and Chinese fly ashes will also be examined.