A new device for measuring an acceleration in a fuel rod has been developed. The primary purpose is to apply it to the experiments for a nuclear fuel fretting, which is caused by a fuel rod and grid interaction due to a flow-induced vibration of the rods. A bi-axial accelerationdetecting device of a cylindrical shape for an insertion into a cladding tube is designed. Two unimorph piezoelectric accelerometers of small size and for special use in a high temperature condition were attached to the housing’s inner wall of the mounting device, which were oriented perpendicularly with each other to accommodate the acceleration signal during a fretting. Verification is carried out by a displacement and a frequency response analysis. The verification results of the bi-axial acceleration-detecting device showed a good response for the amplitude and bi-directional trace. This paper mainly presents the detailed design of the bi-axial accelerationdetecting device which is developed by using the design optimization of a cylindrical type and applying it to the lower and upper plugs to sustain the device in the tube wall. The verification is carried out by a displacement analysis and a frequency response analysis. An elaboration of the development procedure, calibration method and results are also given in this paper.