The existence of natural sulfates in many Middle East aggregates would trigger sulfate attack when they are used in concrete mixture, unless proper precautions are taken. In this study, the effect of sulfates on the expansion of mortars mixed with 2 different sands, contaminated by natural sulfate (water soluble sulfate amounts of 1.6% and 2.0%) provided from Bagdad and Kerbela region in Iraq was investigated. A commercially available Type I cement with C(3)A content of 7.6% was used. The effect of mineral admixtures such as ultra fine amorphous colloidal silica (NS), micro silica (MS), fly ash (FA) and ground granulated blast furnace slag (GGBS) on the expansions caused by internal sulfate attack was monitored. Results have shown that depending upon the percentage used, all of the mineral additives, particularly GGBS, have significantly reduced the expansions. Another significant data was obtained from the samples mixed with NS. Although very low replacement ratios such as 4% to 6% are used, the effectiveness of nano silica is very significant.