In this paper, an experimental investigation was carried out to study strength, toughness and microstructural properties of early age cemented tailings backfill (CTB) reinforced with three different types of fiber. Polypropylene, polyacrylonitrile and glass fibers were used in CTB to better understand the effect of fiber addition on the backfill's strength and toughness properties. Different fiber contents (0 wt%, 0.3 wt%, 0.6 wt% and 0.9 wt%) and curing times (3 and 7 days) were designed for the preparation of CTB samples with two cement-to-tailings ratios (c/t = 1:4 and 1:6). The results indicated that the addition of different type and content of fibers caused a significant change in CTB's toughness. The fiber content influenced the backfill's strength performance. The strength gain of fiber-reinforced CTB samples showed an increasing trend as the fiber content rises. Linear relationships could be used to express relations between strength gain and fiber content. The peak strain factor K was defined during the toughness tests. K showed a monotonous increasing trend by the increase of fiber content. The polypropylene fiber was larger than polyacrylonitrile, but less than glass fiber when fiber content was 0.3 wt%. The unreinforced CTB samples were mainly parallel to the axial tensile cracks and a small amount of shear cracks, while the deformation of fiber-reinforced CTB was relatively large, it did not break into small pieces. The crack resistance of fiber-reinforced specimens was notably better than that of unreinforced ones. Failure mechanism and modes of fiber addition in CTB samples were also studied. As a result, this study could provide a theoretical/application basis for mines to reduce cement usage within the CTB matrix, achieve safe mine production, increase ore extraction and reduce ore losses and dilution. (C) 2019 Elsevier Ltd. All rights reserved.