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This study investigates the experimental laboratory work of concrete to determine the optimum amount of limestone powder to be used in concrete mixes. To handle this purpose 30 concrete cubes were prepared for testing to achieve a compressive strength of 25 MPa According: ASTM (211.1-81). The samples were classified into four different categories according to the ratio of the limestone powder that added to the specimens such as follow; 0%, 1%, 2%, 10% and 15% of cement ratio. For all tests, the cubes were left in curing until testing at the age of 3, 14 and 28 days respectively. The specimens were loaded to failure and the averages of compressive strength were used for comparison purposes. To measure the workability flow table test has been conducted on the fresh concrete directly. Results were compared to null limestone powder samples and revealed that the average compressive strength of samples with ratio 2% was increased by 5% and 9.5% at age 14 days and 28 days respectively. On the other hand, adding 15 % of limestone powder causes significant reduction of compressive strength 43% and 28% and age 14 days and 28 days respectively. The flow table tests revealed an increment in the workability of fresh concrete with 0% a, 1% and 2% of limestone powder used in concrete mixes. An ideal ratio of limestone powder is 2% was recommended in this research study. Keywords: Limestone Powder, Compressive Strength, Flow Table, Workability.