A novel fiber-optic refractive index (RI) sensor based on a splicing point tapered fiber Michelson interferometer is proposed. It consists of a short section of thin-core fiber (TCF), which is spliced to a standard single-mode fiber, then the fused region is drawn into a taper by using residual heat. The interference between the core and cladding modes in the TCF is utilized, which is insensitive to variations in the RI of the surrounding environment but susceptible to external temperature changes. However, owing to the Fresnel reflection on the fiber end face, the intensity of the reflection spectrum decreases with increasing RI of the surrounding environment. Thus, the RI and temperature can be demodulated by the intensity and wavelength of the reflection spectrum, respectively, which can eliminate the crosstalk between RI and temperature. We experimentally found that the sensor has RI sensitivity of up to 68.60 dB/RIU for a TCF length of 10 mm and a waist diameter of 50 µm. The temperature characteristics of the sensor in the range of 30 to 90 ℃ were also investigated, and a sensitivity of about 57 pm/℃ was obtained. Moreover, the compact size, easy fabrication, and low cost of the proposed fiber-optic RI sensor make it an attractive device.