The purpose of the present experiments is to consider the relations between colour-change and crystalline phases of hard oxidizing fire iron red glaze by quenching temperature during firing. The colour of fired samples was analyzed by UV-vis spectrometer and compared with the values of L^*a^*b^*. The result of the experiments showed that the values of L^*a^*b^* had changed remarkably at 1050-950°C, without any observed radical change. Changes in crystalline phases with quenching temperature, whitlockite-type crystals already appeared with firing at 1050°C. Magnesioferrite crystal that was related to the red colour appeared at 950°C upon cooling process and became more clear at 850°C. However, because fine red spots were observed on the surface of sample quenched at 1050°C, it could be considered that the main reaction influencing on coloration had occurred at 1050-950°C. Therefore it is desirable soaking or annealing at 1050-950°C to obtain a prompt crystallization.