Numerous types of floating breakwaters have been proposed, tested and commercialized in the past decades. The majority of these breakwaters are made of solid bodies; hence, they are relatively bulky and are not readily to be rapidly installed at the targeted sites when immediate wave protection of the coastal and offshore facilities is needed. Furthermore, the application of these hard floating structures at the recreational beaches is rather unlikely due to potential deadly marine traffic collision. To overcome these problems, a flexible air-filled wave attenuator (AFWA) has been developed in the present study. This floating breakwater is made of flexible waterproof membrane materials. The main body consists of a rectangular air-filled prism and is ballasted by sandbags located around the floating module. The objective of this study is to evaluate the wave transmission, wave reflection, energy dissipation, motion responses and mooring forces of the AFWA under the random wave actions using physical modelling. The test model located in a 20 m long wave flume was subjected to a range of wave heights and periods. The wave profiles in the vicinity of the test model were measured using wave probes for determination of wave transmission, reflection and energy loss coefficients. The motion responses in terms of heave, surge and pitch, and wave forces acting on the mooring lines were measured using a motion tracking system and load cells, respectively. The experimental results reveal that the AFWA is effective in attenuating up to 95 in the incoming wave height and has low-wave-reflection properties, which is commendable for floating breakwaters. © 2022, Shanghai Jiao Tong University.