This research investigates the effect of silica fume on different mechanical properties of slag cement concrete. Twenty-seven different concrete mixes with various percentages of silica fumes were prepared. The variables include silica fume percentage, water/cement ratio (W/C), cementitious-materials content (slag cement + silica fume) and coarse aggregate type. The test results showed that the use of silica fume as a partial replacement of portland slag cement by weight, improved considerably concrete strengths and the optimum percentage of silica fume that gives the maximum values of ultrasonic plus velocity, compressive, splitting tensile flexural, and bond strengths is 15%. Results have shown, it can be improved concrete strengths clearly by decreasing the WIC ratios, increasing the cementitious materials content and use crushed dolomite as a coarse aggregate instead of gravel.