Fiber-optic thermometry based on temperature dependence of thermal radiation from Tm3+ ions was studied using Tm end doped SiO2 fiber sensor. Visible light radiation peaks due to f-f transition of Tm3+ ion were clearly observed at λ = 690 and 790 nm from Tm end doped SiO2 fibers sensor at the temperature above 600 °C. Thermal radiation peaks are assigned with f-f transition of Tm3+ ion, 1D2-3H6, and 1G4-3H6. Peak intensity of thermal radiation from Tm3+ ion increases with temperature. Intensity ratio of thermal radiation peaks at λ = 690 nm against that at λ = 790 nm, I790/690, is suitable for the temperature measurement above 750 °C. Two-dimensional temperature distribution in a flame is successfully evaluated by Tm end doped SiO2 fiber sensor.