A Serial of Experiments Were Carried Out to Investigate the Efficiency of Waste Tire Rubber on Consistency and Rheological Behavior of Cementitious Materials at Fresh State and on the Mechanical Strength at Hardened State Was Evaluated. Results Indicate that the Addition of Rubber Aggregates Significantly Influences Yield Stress of the Sample in the Fresh State and the Compressive Strength at 28 Days, Depending on the Grain Size Distribution of the Rubber Aggregate and its Volume Percentage in the Mixture. the Yield Stress of the Sample in Fresh State is More Influenced by an Increasing Volume of Rubber Compared to Adding Sand with Equal Grain Size Distribution. the Percentage of Reduction of Compressive Strength of Cementitious Materials Caused by Increasing the Volume of Rubber Aggregates by 1% is About 4.5%.