Heat resisting low expansion zirconyl phosphate-zircon composite bodies are disclosed, which contain zirconyl phosphate and zircon as a main crystalline phase and a secondary crystalline phase, respectively. The heat resisting low expansion zirconyl phosphate-zircon composite bodies have a coefficient of thermal expansion in a temperature range from room temperature to 1,400.degree. C. being not more than 30.times.10-7/.degree. C. and a melting point being not less than 1,600.degree. C. The composite bodies have a chemical composition essentially consisting of 58.2 to 65.4% by weight of ZrO.sub.2, 17.4 to 37.1% by weight of P.sub.2 O.sub.5, and 1.5 to 19.0% by weight of SiO.sub.2. The heat resisting low expansion zirconyl phosphate-zircon composite bodies optionally contain MgO and Al.sub.2 O.sub.3 in a total amount of not more than 2.5% by weight or 0.1 to 4% by weight of Nb.sub.2 O.sub.5. A process for producing such zirconyl phosphate-zircon composite bodies is also disclosed.