A heating experiment was performed at elevated temperatures with a fused-silica-core optical fibre to use it as a temperature measurement sensor in a radiation environment. The results without irradiation are as follows: the optical fibre had characteristic thermal luminescent peaks at 1260 and 1390 nm that were attributed to thermal luminescence of hydroxyl (OH) in silica fibre; further, the peak intensity of OH had a temperature dependence up to 1000°C. The thermal luminescent spectral shape at 900°C remained constant under 60Co γ-ray irradiation; however, luminescence, except for the OH luminescence due to the thermal radiation of the heater, was generated at 1000°C. Therefore, the optical fibre could be used as a temperature measurement tool at 900°C under 60Co γ-ray irradiation. However, the intensity of OH increased with elapsed time, increasing at elevated temperatures. It is necessary to use a temperature-resistant jacket and/or sheath to prevent reaction with air. A partially replaced core optical (PARCO) fibre consisting of a fibre doped with high OH content and sandwiched with pure silica fibre was proposed to have a spatial resolution. The thermal luminescent intensity of PARCO fibre also showed a temperature dependence up to 900°C, and the spectral shape remained constant when the temperature was maintained at 900°C under γ-ray irradiation. The PARCO fibre is a temperature measurement sensor candidate in a radiation field.