Magnesium oxide is one of the most products that used as fuel additive in the treatment of heavy fuel oil. It has a good efficiency in the reduction of the bad effects produced from burning heavy fuel oil.In this work, extraction of magnesium oxide from wastewater of cation exchange regeneration unit was studied. The extracted magnesium oxide was suspended in a solution of gelatin as a suspension agent. Different doses of suspended magnesium oxide were added to heavy fuel oil. The optimum dose for maximum reduction of the free sulfuric acid (acidity) exists in the combustion products was determine, also emission produced from burning treated and untreated heavy fuel oil were investigated. By this treatment, the values of sulfur, sodium and vanadium in the fuel were reduced, while physical properties of fuel were approximately stable. The amount of reduction of some pollutants between treated and untreated heavy fuel oil was calculated. However, sulfur in heavy fuel oil was reduced from1.6 to1.2 ppm with a percent reduction of 25%. The vanadium was reduced from 48 to37 ppm with percentage reduction of 9.1% and sodium was reduced from 84 to 74 ppm with a percentage reduction of 11.9 %, also the value of free sulfuric acid is reduced from 67 to 50 ppm with percentage reduction of 28% and this is an indication for the reduction of SO_X emission.