Abstract: From the viewpoints of fiber morphological structure and surface friction, the compressional behavior of five fiber assemblies has been investigated sequentially by one-way compression, i.e. wool, cashmere, acrylic, goose down and kapok. Fiber morphological structure was one of the main influence factors for the compressional behavior of fiber assemblies. The conclusion that the contact numbers between fibers had nothing to do with the fiber crimp and cross section was verified. Simultaneouly, the compressibility of fiber assemblies depended on fiber arrangement intensively. Different arrangements led to different assembly structures and different sources of compressing force. In addition, there were distinct discrepancy for the forces compressing on the fiber assemblies in cylinder and without cylinder. It depended on that whether the assemblies could swell and deform freely.