The effect of composite rebar's shape in reinforced concrete beam-type structures on the natural frequencies and modes shapes is investigated through finite element analysis in this paper. Steel rebars are being replaced with composite rebars due to their better ability to resist corrosion in reinforced concrete structures for many infrastructure applications. A variety of composite rebar shapes can be obtained through the pultrusion process. lt will be interesting to investigate their shape on free vibration characteristics. The results of natural frequencies and mode shapes are presented and compared for the different composite rebar shapes. The effects of various boundary conditions for different rebar shapes are also investigated. (c) 2005 Elsevier Ltd. All rights reserved.