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Cordierite precursor was obtained through a process, which involved the decomposition of metal nitrates on the surface of ultrafine carbon black powder between 100-300℃ and the gasification of the carbon black at higher temperature in air. The average size of the particles, which were heat-treated at 700℃ for 10h, is about 1020nm, and the specific surface area is about 129m2/g. The experimental results show that the ultrafine particles of cordierite precursor can be produced by this process. The precursor powder was calcined at different temperatures. X-ray diffraction examination indicates that β-quartz is crystallized from the amorphous matrix around 850℃ firstly and then MgO-Al2O3 spinel and α-cordierite appears. Above 1000℃, MgO-Al2O3 spinel and cristobalite disappear gradually and form an intermediate phase (sapphirine). At around 1300℃, the main phase is α-cordierite, and no other phase is detected.