This investigation examines fibers' physical properties, reinforcing effects and mechanisms for stabilizing and reinforcing asphalt binder. Laboratory tests of water absorption, mesh-basket draindown, and oven heating were designed and performed on five fiber types (two polyesters, one polyacrylonitrile, one lignin and one asbestos), to evaluate their wettability, asphalt absorption and stabilization, and thermostability, respectively. The cone sink experiment was designed to study fiber modified asphalt's resistance to flow, and the standard dynamic shear rheometer test was conducted to evaluate fiber modified asphalt's rheological properties and rutting resistance. Fibers' microstructures and spatial network formed in asphalt binder were observed using Scanning Electron Microscopy (SEM). Results indicate that fibers can effectively improve asphalt binder's resistance to rutting and flow, and dynamic shear modulus. Fiber reinforces asphalt matrix through its functions of spatial networking, adhesion and stabilization of asphalt binder. Polyester and polyacrylonitrile fibers seem to have greater network effect than the lignin and asbestos fibers, and their antenna features at fibers' ends further strengthens this effect. The lignin fiber has the highest water absorption while lowest thermostability. The lignin and asbestos fibers pose greater effects of asphalt absorption and stabilization than do polymer fibers. (C) 2009 Elsevier Ltd. All rights reserved.