This research investigates the effect of silica fume on chemical resistance of slag cenjent concrete. Twenty-eight different concrete mixes with various percentages of silica fume were prepared. The variables include, silica fume percentage, water / cement ratio, cementitbous materials content (slag cement + silica fume) and coarse aggregate type. The test results showed that the slag cement is the best cement for resisting chemicals attack and the use of silica fume as a partial replacement of slag cement by weight improved considerably concrete resistance and the optimum percentage of silica fume that gives the maximum resistafice against sulphate and sea_ water attack after 6 months of immersion is 15%. Results have shown, it can be improved concrete resistance clearly by decreasing the W/C ratio„and increasing the cementitious materials content. Using of crushed dolomite instead of gravel has the same effect in sulphate resistance as gravel concrete and badly effect in sea water resistance. KEWO,RDS Sulphate and sea water resistance; slag cement; silica fume.