Long-period fiber grating (LPFG) is a promising curvature sensor due to its high bending sensitivity. In this article, a fiber ring laser (FRL)-based curvature sensor with an LPFG was proposed and experimentally verified. LPFG acted as both a filter and a curvature sensing element. The maximum measurement sensitivity of curvature reached 7.99 dB/m-1 in a wide range of 4.89–13.33 m-1 which was wider than most of previously reported curvature sensors. The bending and filtering characteristics of LPFG were verified by changing its position in FRL. The output wavelength of the FRL could be tuned through the bending of LPFG. The proposed curvature sensor, showing the advantages of a wide measurement range, high resolution, and high sensitivity, has potential applications in monitoring the deformation of surgical instruments, robot arms, and engineering objects.