The variation of the warp yarn tension in the weaving process causes the irregularity of the weft density of woven fabrics. In particular, the warp yarn tension varies to a great extent when the take-up speed, the let-off speed do not coincide. Therefore it is necessary to maintain the warp yarn tension constant by controlling the let-off speed, considering the take-up speed and warp beam diameter. In general, it is indispensable to know the dynnamic characteristics in order to control a system optimally. Here, the dynamic characteristics of the let-off/take-up process were studied experimentally, using the frequency response method. For the weaving machine developed for this study, the let-off system was driven by a servo-motor. The warp yarn tension was measured by the backrest movement which was in the state of equilibrium with the loading force of a spring. A load cell was connected to the spring. From the experiments it was observed that the test process, namely the interval between the let-off system and the warp yarn tension measurement, had the dynamic characteristics of an integral system and the warp yarn tension could be measured by the movement of the backrest loaded by a spring.