Based on a long-period grating (LPG) formed in a index guiding photonic crystal fiber (PCF) that is filled with a liquid of temperature-sensitive refractive index, a novel temperature sensor is proposed. Using a full-vector finite element method, the modal profiles and the dispersion curves of the core mode and the cladding mode of a large mode area photonic crystal fiber (LMA-PCF) are calculated with their hexagonally arrayed air-holes filled and unfilled with liquid ethanol, respectively. By means of the coupled-mode theory, the temperature dependence of the transmission spectrum of the PCF-LPG is studied. The result shows that in the temperature range from -20 ℃ to 80 ℃ the PCF-LPG resonance wavelength varies almost linearly with the temperature when the PCF is filled with liquid ethanol and the temperature sensitivity is 1.766 nm/℃.