Data from nationwide population-based nutrition surveys in Taiwan were used to investigate trends and nutritional status for magnesium from 1993 to 2008. Dietary magnesium intake was estimated from 24-hour dietary recalls. Serum and urinary magnesium were also measured. In Nutrition and Health Survey in Taiwan (NAHSIT) 2005-2008, average magnesium intake was 305 mg and 259 mg for adult males and females, respectively, which is equivalent to 82-85% of relevant Taiwanese Dietary Reference Intakes (DRIs). After correcting intra-individual variation, 74-81% of adult subjects' dietary magnesium was estimated as sub-optimal. Mean serum magnesium concentration was 0.866 mmol/L and 0.861 mmol/L for the males and females, respectively. The prevalence of low serum magnesium (<0.8 mmol/L) was 12.3% and 23.7% for the males and females, respectively. There was positive association among dietary magnesium, blood magnesium, and urinary magnesium/creatinine ratio. From NAHSIT 1993-1996 to NAHSIT 2005-2008, dietary magnesium significantly increased (p<0.05), the blood magnesium and urinary magnesium/creatinine ratio decreased (p<0.05). The findings suggest that the relationships between dietary magnesium and biochemical markers among different nutrition and health surveys are not straightforward and need to be further clarified.