Concrete is a composite material of which 60-75% by volume is aggregates. Out of this volume, 30-40% is composed of fine aggregates. Fine aggregate is one of the predominant contents of concrete usually natural river sand is used as the fine aggregate. Currently, a shortage of river sand has become a problem for the construction industry in Ethiopia. Therefore, replacing this material with another available substituting material is a must.rnThe objective of this experimental study was to investigate the effect of using scoria as an alternative for fine aggregate in concrete. Detail experimental investigation has been carried out to understand the behavior of concrete when scoria replaces sand. Concrete mix design was prepared for C-25 classes of concrete using ACI mix design procedure. The fine aggregate was replaced by scoria at 35%, 50%, 70% and 100% by volume. The control mix without incorporation of scoria was prepared which was used as reference for comparison of test results with those specimens produced by partial replacement.rnThe research studied the chemical composition and chemical phases of scoria, microstructural analysis of sand and scoria and for the fresh and hardened concrete; workability, density, compressive strength, flexural strength, split tensile strength, ultrasonic pulse velocity test and water Penetration tests has been done for 7, 28 and 56 days of curing age.rnThe results are quite encouraging with these supplementary materials in the concrete. Based on the analysis with XRD and SEM it was identified that the main phases present on scoria sample are glassy form which is amorphous. And Considering the SEM analysis to determine the apparent porosity, in this paper only the effect of magnification is considered and the result obtained for apparent porosity on magnification 1000X for scoria sample is 41.427% and for sand 35.504%.rnThe slump of the concrete decreased through percentage replacement of sand with scoria and also the density of concrete decreased with the percentage replacement of sand with scoria. The water penetration of concrete decreased as compared to the control mix.The investigation of this thesis has revealed that compressive strengths of concrete mixes with 35%, 50%, 70% and 100% sand with scoria replacement satisfy the ACI Specifications for Structural Concrete. The strengths achieved for the 28 days of curing age are 35.63, 35.58, 33.15 and 31.03MPa respectively and for the 56 days are 43.6, 38.61, 36.85 and 33.61 with this the optimum percentage 35% was selected. It is known that the concrete quality highly depends on the compressive strength therefore from the results of the ultrasonic test it is shown that the percentage substitution with 35% gives a higher pulse velocity that is in a good agreement with that of the compressive test result.rnEven if there is a variation in flexural strength, the optimum is seen when sand replaces scoria with 50% with a value of 4.88MPa. And there is also a variation on the tensile strength of concrete and the maximum tensile strength attained is at a replacement of 50% scoria with a value 3.36 MPa which is higher than that of the control specimen so we can say that adding scoria in concrete will enhance the tensile strength of concrete to develop.