An all-optical fiber curvature sensor is proposed, which is composed of a polydimethylsiloxane elastic material encapsulated all-optical fiber Mach–Zehnder interferometer, and its bending characteristics are demonstrated. Our experimental results show that the output spectrum of the sensor is sensitive to the curvature of the bend angle with a result of interferent dip wavelength drift with it. The curvature sensitivity of the sensor presents 205.36  nm/cm^−  1 with 98.27% linearity in the curvature range from 0.03 to 0.08  cm^−  1. The temperature sensitivity is 0.1235  nm  /    °  C in 35°C to 105°C range. This sensor structure also has the advantages of small size, low cost, and easy fabrication, which means it has potential applications in robots, artificial intelligence, aerospace, and so on.