Coal briquette ash is an inorganic and non-combustible material. Although coal briquette ash is mainly composed of SiO2, Al2O3, and is an acceptable raw industrial material (containing Fe2O3, K2O, MgO, CaO, TiO2, and Na2O), it is merely considered waste and is exploited as a building material for concrete admixtures and bricks. Because mullite (3Al2O3 2SiO2), which coal briquette ash contains, is a stable compound with a crystalline structure, it plays essential roles in its fracture strength and bending strength. This study serves the purpose of developing environmentally friendly, economical clay bodies through the use of coal briquette ash as a substitute for kaolin to provide Al2O3 and SiO2. We also investigated the seed effects during sintering process by feeding mullite directly into clay bodies. The results show that in 1,300°C heat, a mixture of 40% coal briquette ash, 40% feldspar/limestone (8 : 2), and 20% clay indicates a fracture strength value of 525 kgf/cm2, an absorption rate of 0.72%, burning shrinkage of 11.5%, and an average bending strength of 0.6 cm, which is superior to other clay bodies. The addition of coral briquette ash in clay bodies promoted mullite formation and grew as mullite acted as a seed. In addition to the developing clay bodies, it can also make an oatmeal-colored glaze to widen the spectrum of its usability. This study will help resolve waste problems, reduce environmental pollution, and raise economic value by using coal briquette ash as a raw material for ceramics. Clay bodies made with coal briquette ash are expected to continuously contribute to the development of the ceramics industry with upcycling effects.