An optical fiber inclinometer comprises a pair of fiber Bragg grating devices, a fixed base, a connection plate, and a rotatable base. One end of the connection plate is fixed to the fixed base, whereas the other end of the connection plate is connected to the rotatable base through the joint of a turning pair mechanism between them. The two ends of each fiber Bragg grating device are installed onto the fixed base and the rotatable base respectively, and the two devices are mounted on the opposite side of the connection plate. Once the rotatable base rotates around the joint of the connection plate, axial tensile elongation occurs in one of the fiber Bragg grating devices, whereas axial compressive deformation occurs in the other device. The rotation angle of the rotatable base relative to the connection plate can be obtained by measuring and calculating the Bragg wavelength drifts of the pair of fiber Bragg grating devices respectively.