The purpose of this study was to investigate magnesium nutritional status and its association with asthma in elementary school children (1277 boys and 1109 girls) participating in the Nutrition and Health Survey in Taiwan (NAHSIT children 2001-2002). Dietary magnesium intake was based on 24-hour dietary recalls. Serum magnesium was measured. Average magnesium intake was 247 mg and 228 mg for the boys and girls, respectively, which is equivalent to 135-123% of the relevant Taiwanese Dietary Reference Intakes (DRIs). Mean serum magnesium concentration was 0.87 mmol/L and 0.86 mmol/L, respectively. The prevalence of serum magnesium <0.8 mmol/L was 10.5-13.5% in both gender in our sample of elementary school children. In Taiwan, asthma was diagnosed in about 5.8% and 4.7% of boys and girls, respectively. In this study, there were no associations between asthma prevalence, dietary magnesium and serum magnesium concentration. In about 40% of our sample of school children, however, dietary magnesium may be suboptimal. This deficit should be targeted though improved intake of magnesium-rich foods such as whole grains, green vegetables and soybean products, particularly in Taiwanese school children whose dietary intakes are below the DRIs and/or who have low serum magnesium levels.