We design and demonstrate a temperature sensor based on an ethanol-sealed double helix microfiber coupler (DHMC). The sensor consists of two intertwined microfibers with a minimum waist diameter of up to 3.4  μm. The temperature sensitivity of the DHMC can reach up to −2.03  nm  /    °  C in the range of 25°C to 55°C due to the thermo-optic effect of ethanol and the thermal expansions of the sealant and sealed liquid. Effects of different mechanisms on the temperature sensitivity are also investigated theoretically and experimentally. By encapsulating the coupler in a capillary, the mechanical strength and environmental anti-interference of the sensor are greatly improved. Moreover, the device with easy fabrication, compact size, and low cost is suitable for temperature measurement in most environments.