Abstract In this paper, a fiber curvature sensor based on single-mode fiber (SMF) taper structure in combination with fiber loop ring down (FLRD) technique is proposed. The curvature is sensed by the ring-down time altered by the bending loss of the SMF taper with different curvature. In the experiment, five SMF tapers with waist diameters from 44.1 to 65.4 μm were tested, with the curvatures in the range of 0–8.33 m−1. The sensitivity of the SMF taper with 44.1 μm and 65.4 μm waist diameters were 0.725 μs/m−1 and 0.328 μs/m−1 respectively. Then the way of comparing the sensitivities with different units was supposed. Compared with other curvature sensors, the system has the advantages of simple structure, high sensitivity and low cost.