Composites consisting of fique fibers ( Colombian fibers) and unsaturated polyester ( UP) matrix have been investigated. Fique fiber bundles were subjected to alkalization and/or treated with different chemical agents such as maleic anhydride, acrylic acid and a silane to provide increased compatibility between fiber and resin. The mechanical behavior of the composite materials was analyzed by flexural tests. Maximum mechanical properties were observed for composites with fibers subjected to alkalization and also when it was applied as previous process for the other treatments. Aspects of composite materials such as fiber bundle length, fiber content as well as two ways of preparing the material, lamination and BMC, have been evaluated. The influence of surface treatment of fiber on curing of the polyester resin was analyzed by differential scanning calorimetry (DSC). Dynamic mechanical properties were also evaluated to establish the influence of the interfacial interactions on the mechanical behavior of the laminates. (C) 2004 Kluwer Academic Publishers.