Use of structural lightweight concrete is preferred since the dead load of concrete buildings is enormous. A lower density of the lightweight concrete decreases the weight of the building. Statically, it decreases the earthquake loads, minimizes the sizes of the load bearing structural members and contributes into more economical solutions of the foundation problems. Lightweight concrete, having a lower module of elasticity, has a faster rate of crack development in reinforced concrete members. However, steel fibers are employed as an additive to the concrete in order to increase the energy absorption capacity and to control the crack development. Based on these ideas, steel fibers were added to the lightweight concrete and their effects on the behaviors of concrete and reinforced concrete beams were investigated. For this purpose, lightweight concrete and reinforced concrete beam specimens were produced with the addition of steel fibers in different strengths and ratio. The specimens were tested on four points through loading experiments and their utility for building members was investigated. As a result of the study, it is found that steel fiber addition increased the toughness capacity of prismatic concrete beams and their ductility. It also increased bearing strength and ductility of the reinforced concrete beams. Through this experimental study, the performance of the reinforced concrete beams was increased with the addition of steel fibers. It was also concluded that the decrease in the dead load with steel fiber added lightweight concrete can be considered for reinforced concrete beam designs. (C) 2012 Elsevier Ltd. All rights reserved.