The development of new temperature-dependent phosphor particles for high temperature thermometry is presented. To develop the phosphor material that can be applied to the intensity ratio method, the photoluminescence of Y 2O 3:Tb,Tm was investigated with elevating temperature. As a result, Y 2O 3:Tb,Tm phosphor shows that the peak intensity at 456 nm is still strong at more than 1100 K whereas the other peak intensities decrease due to the thermal quenching. Thus, the intensity ratio I 543nm/I 456nm has a high gradient and linearity over a wide temperature range, and it is confirmed that Y 2O 3:Tb,Tm provides a higher resolution in temperature measurement than Y 2O 3:Tb and Y 2O 3:Tm. Also, since this phosphor changes its emission color from green to blue with increasing temperature, it is possible to measure temperature not only by analyzing the intensity ratio but also by observing the color change in appearance. It can, therefore, be expected to use as a Visual Thermo-Sensor (VTS).