A luminescent properties of a phosphor material, Y2O2S:EuSm, was investigated. A temperature sensitivity of the spectral shape was only 0.008%/°C. That of the luminescent lifetime was 0.78%/°C in a range of 50∼210°C. A lifetime based phosphor thermometry was performed using simple experimental setup composed of a non-intensified high speed CMOS camera, a single-pulsed UV laser and a phosphor coated with a thin metal film. The proposed system makes it possible to measure an instantaneous wall temperature even in a combustion chamber. It was demonstrated that the effect of the excitation power on the phosphor lifetime was small and that the coated metal film never affected to the phosphor lifetime. The temperature uncertainty was ±4.4°C which was evaluated from the measurements of temperature uniform fields. Then, the instantaneous wall temperature measurement was demonstrated in a severe condition with a combustion flame in the RCEM. The measured temperatures were qualitatively correct.