An optical fiber temperature sensor based on optical fiber coupler and evanescent wave is presented. The overall goal of our research is to design a temperature sensor system which is used to monitor temperature accurately. Coupler is used as the sensor probe. Such kind of coupler uses standard communication SM fiber to be a sensing component of evanescent wave. The probe is obtained by replacing the cladding of coupler region with temperature sensitive material. The whole system is then exposed in a thermal bath. A numerical modeling of the sensor based on supermode theory is studied and the result is simulated. At last, the system for temperature measurement in experiment is simply described.© (2005) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.