Abstract: High-temperature saturated steam was firstly applied to pre-treat fresh moso bamboo (Phyllostachys pubescens Mazel ex H. de Lehaie) culms with high moisture content, and then bamboo fibers were extracted from the thermal treated bamboo culms by rolling. And then the microstructure, chemical composition, mechanical behavior, and hygroscopic properties of the extracted fibers were analyzed by using optical microscopy, nanoindentation (NI) and so forth. Results indicate that the vascular bundles and parenchymatous cells in bamboo culms have been effectively seperated due to the degradation of hemicellulose after the steam and mechanical treatment. The degradation of hemicelluloses, increaed relative lignin content and cellulose crystallinity (C_rI) upon thermal treatment make a major contribution to the reduced hygroscopicity and increase of reduced elastic modulus (E_r) and hardness (H) of fiber cell walls. The maximum tensile strength and modulus of bamboo fibers are 765 MPa and 24.8 GPa, respectively, which are not obviously affected by steam treatment. However, there are some differences in the properties of bamboo fibers extracted from different parts in bamboo culms. The dimensions of fibers from outerlayer are larger than that of inner layer and the tensile properties of fibers from bamboo culms without nodes are higher than that of bamboo culms near the nodes. Thus, multilayer extraction and classifiedutilization of bamboo fibers should be considered in its potential application.