An all fiber sensor for simultaneous measurements of refractive index and temperature was fabricated based on Michelson interferometer. The proposed sensor is composed of a single-mode fiber (SMF) core-offset fusion spliced with a thin-core fiber (TCF) with length of 5 mm. The response characteristics of the sensor for the surrounding refractive index (SRI) and temperature variations are theoretically analyzed and experimentally demonstrated. The proposed Michelson interferometer is demonstrated with the sensitivities of -41.10 dB/RIU and 23.15 pm/℃ for the SRI and temperature variations at the range of 1.333 3~1.404 9 and the temperatures changes at the range of 20~90 ℃.The simultaneous measurements have been carried out via the power-referenced for SRI and wavelength-referenced for temperature. The theoretical analysis of the sensor is in good agreement with the experiment. This kind of sensor, with easy fabrication and high measurement accuracy, can offer the attractive applications to biomedical sensing.