Optical microfibers (OMs) are good alternatives in the field of sensing. In this letter, a simple and effective miniature temperature sensor based on OM is proposed and experimentally verified. Using pure water and fiber coating as the OM clad, an additional loss will occur due to the absorption of outer medium. The temperature of the outer environment can be estimated by monitoring the change in additional loss. In the demonstrated experiments, a series of OM with different diameters, waist lengths, and constructions are used as sensing elements. The correlation coefficients between the experimental results and the linear fittings are better than 0.99, and the temperature sensitivity obtained by the linear fittings can achieve –0.151 dB/oC (in pure water) and –0.405 dB/oC (covered by fiber coating). Moreover, higher sensitivity can be obtained by decreasing the diameter, increasing the waist length of the OM, or choosing the proper operating wavelength.