A type of fiber thermocouple is applied to a brush seal in order to obtain the temperature of the bristle-rotor friction zone. Using a brush seal test rig, the temperature measurements utilizing a fiber thermocouple, infrared thermometer, and common thermocouple are compared and studied. The fiber thermocouple is studied under various operational conditions consisting of different pressure and speed variations, rotor-bristle interferences, and eccentricities. Some interesting phenomena and characteristics of brush seals are revealed during these experiments. Some preliminary wear results of a fiber thermocouple are also presented. The results demonstrate the superiority of fiber thermocouples when used in narrow spaces, high temperature, and pressure environments within the heart of an aero-engine.