Aim: Coronary slow flow phenomenon (CSFP) is a microvascular circulation disorder. It is known that serum magnesium has positive effects on anti-inflammation, vasodilatation and endothelial functions. This observational study investigated the association of serum magnesium levels with CSFP.Materials and Methods: Patients who had undergone coronary angiography (CAG) after noninvasive testing were included in the study. CAG records were reassessed for CSFP and 100 patients were diagnosed as having CSFP. Control subjects (n = 80) had normal coronary flow. Serum Mg levels and other biochemical parameters such as glucose, creatinine, cholesterol levels and hemoglobin samples were collected before CAG. Serum Mg values were categorized into two groups: Mg levels equal/under and above 1.9 mg/dL.Results: The mean patient age was 56.1±9.7 years; 68.9% of patients were men. Patient’s hypertension, diabetes mellitus history and smoking habits rate were similar between groups. Biochemical tests revealed lower serum magnesium levels (1.87 vs 1.95mg/dL, p=0.02) for CSFP patients and controls, respectively. In multivariate regression analysis, a serum magnesium level under 1.9 mg/dL (OR:3.33, 95% CI:1.75-6.37, p<0.001) and male gender (OR:2.08, 95% CI: 1.016-4.34, p=0.04) were found to be independent predictors of CSFP.Conclusion: Low serum magnesium levels were associated with CSFP. However, these results are not sufficient to fully determine the role of Mg levels in the mechanism of CSFP-related chest pain.