BACKGROUND: Minerals are essential materials in animal reproduction. The determination of these elements is valuable in relation to different conditions in Arabian horses. OBJECTIVES: The purpose of this study was to evaluate the effects of pregnancy on certain macro and micro minerals in Arabian horses. METHODS: Blood samples were collected from one hundred apparently healthy mares from different regions of Ahvaz including 50 pregnant mares (light, medium, heavy) and 50 non-pregnant mares. Macro-minerals (calcium, phosphorus, magnesium, sodium and potassium) and micro-minerals (copper, zinc and iron) were measured, using standard common laboratory methods. Methods of O-cresol phetalein, Molybdate reduction, Xylidil blue were used for measurement of calcium, phosphorus and magnesium respectively. Flame photometry was used for measurement of sodium and potassium. Amounts of copper, zinc and iron were measured by atomic absorption spectroscopy.  RESULTS: In order to analyze the results, all the data was statistically compared by SPSS-17.0 software. The study of serum calcium levels between the pregnant and non-pregnant mares showed that the differences were not significant. In this study there was significant differences between serum phosphorus levels between pregnant and non-pregnant mares (p<0.05). The serum phosphorus levels during different stages of pregnancy was significantly different (p<0.05), and the level of serum phosphorus during pregnancy declined in total compared to non-pregnant mares. Serum magnesium did not show significant differences between two groups. Serum sodium levels, compared to the other two groups, did not show significant changes. Changes in serum potassium levels showed significant difference between two groups of pregnant and non-pregnant mares (p<0.05). The level of potassium in pregnant mare’s serum was less than non-pregnant, and the least level of this element was seen in medium pregnancy. CONCLUSIONS: Except phosphorus, potassium and zinc, other minerals did not affected different stages of pregnancy. Although the relationship between these changes and pregnancy can be the result of physiological processes, the other factors such as parity, age, nutrition, season, weather conditions and other factors should not be ignored in the evaluation.