The clinkerbility and the behaviour of formation of $3CaO{cdot}Al_{2}O_3$ were studied using the mixture of waste oyster shell and spent oil-refining catalyst mainly by the mineral and microstructural observation. By virtue of the formation of $12CaO{cdot}7Al_{2}O_3$ at relatively low temperature and its successive reaction with CaO, the $3CaO{cdot}Al_{2}O_3$ clinkers were formed easily without affection of minor constituents contained in oyster shell. Thus clinkers were formed at $1400^{circ}C$ directly but began to melt incongruently at higher temperature above that. Aluminium hydroxide, however, was not desirable as an aluminous raw materials of the clinker because rapid melting occurs before $3CaO{cdot}Al_{2}O_3$ forms main clinker mineral.