PURPOSE: To provide a mullite oxide ceramic whose strength and tenacity are superior, whose mechanical workability is good and whose dimensional shrinkage is extremely small, as a raw material for structural, electronic and medical use.

CONSTITUTION: The strength and tenacity are enhanced by an oxide based ceramic which incorporates ≥20wt.% mullite crystal phase composed of an accicular or columnar crystal and which is arrayed at random in the matrix, and easy workability is enabled to be imparted. The method of sintering a molded body consisting of a silimanite mineral, a glass component and a metallic oxide at the temp. over the heat decomposition temp. of the silimanite mineral, is useful to produce the ceramic. Thus the cost is reduced because of superior workability, the dimensional accuracy is excellent, and it is endured for a long period use because of high strength and tenacity.