A temperature sensor based on the octagonal-lattice photonic crystal fiber (PCF) is designed. All the air holes are assumed to be filled with temperature sensitive liquid. The temperature sensing characteristics are analyzed by finite element method (FEM). The phase birefringence, the group birefringence, and the sensitivity dependence on the operating wavelength λ are studied. The temperature is varied from 25 °C to 85 °C and at 25°C and at 1.55 μm wavelength, we obtain phase and group birefringence values of -6.4×10-5 and 7.7×10-5 respectively. The sensitivity reaches as high as -9.5 nm/°C at 35°C and 1.8 μm wavelength. The effect onsensingcharacteristics of the temperature sensor by altering the diameter of the two central big air holes is also analyzed. Good birefringence values are obtained for r1 value of 3.4 μm. © 2017, Institute of Advanced Scientific Research, Inc. All rights reserved.