Concrete is the most generally used construction material in buildings,pavements, and infrastructures. Concrete is a construction materialcomposed of cement as binder, fine aggregates and coarse aggregatesmixed with water which hardens with time. Concrete is a versatileconstruction material within the housing industry of the planet. Thestandard of the concrete is tormented by various factors and from thosevarious factors which may have an effect on the concrete quality are, thecoarse combination size has its own nice role on the standard of concreteproduction. A laboratorial experiment was conducted to work out the resultscoarse aggregates size on recent and hardened concrete properties. For thisstudy totally different crushed volcanic rock aggregates sizes were collectedfrom almost Jimma city for determination of the results of coarse aggregatesizes in concrete production. Three coarse aggregate nominal sizes of 10mm, 14 mm and 20 mm were used for samples production to envision thescale effects on concrete properties. For this study the procedures that wasfollowed, the types and quantity of materials for concrete creating weresimilar whereas sizes of nominal basaltic coarse aggregate were different.The fresh concrete has a slump value of 67 mm, 72 mm and 83 mm for10mm, 14 mm and 20 mm aggregate sizes respectively. A total of thirty sixconcrete cube samples were ready and tested using compressive strengthtesting machine at totally different ages of the cube 7 days, 14 days, and 28days, to know their strengths. The compressive strength was 23.524 Mpa,22.643 Mpa and 22.41 MPa for aggregate sizes of 10 mm, 14 mm and 20mm respectively. The laboratory results show that 10mm coarse aggregatesize gave the most effective compressive strength and comparativelylowest slump at similar water/cement ratio of 0.6. At 28th day 10mmcoarse aggregate size gave 23.524 Mpa compressive strength which is themaximum compressive strength from the remainder coarse aggregates so,the optimum maximum size of coarse aggregate for this study was 10mm.