Abstract：The content of calcium and magnesium in the filtrate which was obtained in the determination of silicon dioxide by gravimetric method during the system analysis of iron ore was determined by EDTA complexometric titration. The content of calcium oxide and magnesium oxide in iron ore was thus calculated out. The method did not require separation of interference elements such as iron, aluminium, titanium, copper, nickel and manganese in iron ore. The interference could be eliminated through adding sodium potassium tartrate tetrahydrate, hydroxylamine hydrochloride or triethanolamine in acid solution, or adding cupferron in ammonia solution. In ammonia solution, the acid chromium blue K - naphthol green B was used as indicator to determine the total amount of calcium and magnesium by EDTA standard solution titration. Then, KOH solution was added in the same solution to determine the released EDTA from EDTA-Mg complex with calcium standard solution using calcon as indicator. Meanwhile, the EDTA/Ca comparison test was conducted to obtain the comparison coefficient. The content of magnesium oxide was calculated according to the comparison coefficient, consumed volume of calcium standard solution during the titration of released EDTA and the amount of sample. Then, the content of calcium oxide could be calculated by subtraction. The proposed method was applied to the parallel determination of calcium oxide and magnesium oxide in iron ore standard sample. The results were consistent with the certified values. The relative standard deviations （RSD, n=6） of determination results were 1.1 %-4.0 %. The recoveries were 98 %-104 %.
