The polarization-maintaining properties of single crystal sapphire fibers are investigated and a polarimetric optical sensor for high temperature measurements is designed. The polarization-maintaining properties of single crystal sapphire fibers are investigated experimentally for different modal power distributions and different fiber lengths. Experimental results indicate that linearly polarized light launched along one of the principal axes of the birefringence can be partially maintained. The polarization-maintaining ability (PMA) has been measured to be 6 dB and 3 dB for 7 cm and 32 cm long sapphire fibers, respectively. The temperature coefficient of the differential phase delay between the orthogonal polarization modes has been measured to be 0.0208 rad / °C m. A resolution of 2 °C has been obtained over the measurement range of 25 °C to 800 °C. It is also observed that the PMA is strongly dependent on the mode-coupling parameter. The design of the polarimetric sapphire fiber sensor for high temperature measurements is based on the properties of withstanding high temperatures, polarization preservation and temperature dependence of phase delay. Since the temperature dependence of phase delay is proportional to the fiber length, consideration of a similar strain sensor is expected in the near future.