This investigation demonstrates the feasibility of using diatomite and coal fly ash as alternative raw materials in the production of the porous ceramics. The following operating conditions are set for sintering process; a constant pressure of 5 MPa, a sintering temperature of 1000–1270°C, a sintering time of 2 h, and various proportions (0–20%) of coal fly ash in waste diatomite. This investigation concerns the effects of heating temperature and proportion of fly ash on the characteristics of porous ceramics that are formed from a mixture of fly ash and waste diatomite. Heat-treated samples were analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM), and mercury intrusion porosimetry (MIP), which supported the following conclusions. When the heating temperature was increased above 1270°C, the compressive strength of the ceramics was between 5.85 and 15.8 MPa. When the amount of coal fly ash exceeds 20%, the porosity of the porous ceramics decreases sharply with increasing temperature from 61.6% obtained at 1100° C to 52.9% obtained at 1270° C. When heating to 1270° C, the pore sizes of sintered samples ∼2.5–3 μm, and a smaller peak around 0.3–2 μm. Adding coal fly ash to the porous ceramics increased their compressive strength, indicating that waste diatomite and coal fly ash can indeed be 100% recycled and reused as porous ceramics. © 2011 American Institute of Chemical Engineers Environ Prog, 32: 25–34, 2013.