In this study, effects of aspect ratio (l/d) and volume fraction (V-f) of steel fiber on the compressive strength, split tensile strength, flexural strength and ultrasonic pulse velocity of steel fiber reinforced concrete (SFRC) were investigated. For this purpose, hooked-end bundled steel fibers with three different l/d ratios of 45, 65 and 80 were used. Three different fiber volumes were added to concrete mixes at 0.5%, 1.0% and 1.5% by volume of concrete. Ten different concrete mixes were prepared. After 28 days of curing, compressive, split and flexural strength as well as ultrasonic pulse velocity were determined. It was found that, inclusion of steel fibers significantly affect the split tensile and flexural strength of concrete accordance with l/d ratio and V-f. Besides, mathematical expressions were developed to estimate the compressive, flexural and split tensile strength of SFRCs regarding l/d ratio and V-f of steel fibers. (c) 2006 Elsevier Ltd. All rights reserved.