The noticeable brittleness of lightweight aggregate concrete limits its vast application. Using of steel fiber will improve the disadvantage contrived in this type of concrete. Steel fiber increases the ductility and prevention of brittle failure of the concrete. In this paper the influence of steel fiber on the ability of lightweight concrete to absorb energy during deformation in compression has been investigated. For the purpose of this study, 0.0%, 0.5%, 1.0% and 1.5% steel fiber ratios were used by volume of the sample. The sample with 0.0% steel fiber .ratio was used as reference to be compared with samples including steel fiber Two types of steel fiber including hooked-end and crimped were used and all fine and coarse aggregate were lightweight .The results showed that there is no noticeable improvement in pre-peak energy absorption with adding of steel fiber to the composite. Increasing of steel fiber ratio changes the shape of descending branch of stress-strain curve in compression and increases the compressive toughness of lightweight aggregate concrete.The value of the compressive toughness of the plain lightweight aggregate concrete at the strain of 0.009 is about 132kJ/m2. while for 0.5%, 1% and 1.5% steel fiber ratios by volume of sample, the .value is 151, 166 and 176 kJ/m2 respectively
