A novel fiber curvature sensor based on Mach–Zehnder interferometer using up‐taper cascaded long‐period grating is proposed. The variation of the sensor's curvature will change the phase difference of core mode and cladding mode in the sensor, and will finally induce a wavelength shift in the transmission spectrum. By monitoring the wavelength shift, a sensor for bending measurement is achieved. Experimental results show that the curvature sensitivity of the proposed sensor is as high as −12.555 nm/m−1 in the curvature range of 0.706–3.444 m−1. As the curvature increases, the dip wavelength has a blue shift. The curvature resolution of the proposed sensor is about 1.59 × 10−3 m−1. And the temperature effect is also investigated. © 2016 Wiley Periodicals, Inc. Microwave Opt Technol Lett 58:246–248, 2016