A novel fiber-optic Fabry-Perot refractive-index sensor is proposed, which is formed by a section of endlessly single-mode photonic crystal fiber (EPCF) and conventional single-mode fiber. The theoretical and experimental results show that the refractive-index measurement based on the fringe visibility is independent of temperature change, and the refractive-index resolution and sensitivity are about 2×10-5 and 4.59/RIU, respectively, when the refractive index of the environment is in the range of 1.32～1.44. In addition, such a sensor can be used as an excellent temperature sensor with a cavity-length-temperature sensitivity of 18.72 nm/℃ with temperature ranging from 20℃ to 100℃. Therefore, simultaneous measurement of refractive index and temperature can be realized by determination of the fringe visibility and the cavity length change of such anEPCF-based IFPI, respectively. It provides a practical way to measure refractive index with self temperature compensation.