Background and aims: Peripheral arterial disease (PAD) is a clinical manifestation of extracoronary atherosclerosis. Many risk factors are involved in the process of PAD, but the association between serum magnesium (Mg) and PAD is not clear. Our study aimed to investigate whether serum Mg is associated with PAD incidence. Methods: A total of 13,826 participants (aged 40-64 years) in the Atherosclerosis Risk in Communities (ARIC) study (1987-1989) without prior PAD were included in the final analysis. Serum Mg levels were measured at visits 1 and 2. PAD was defined as an ankle brachial index less than 0.9, or hospitalization with a PAD diagnosis. Cox regression was used to calculate hazard ratios (HRs) for incidence of PAD and serum Mg. Results: During a median follow-up of 24.4 years, 1364 (48.4% female) PAD events were observed. After multiple adjustment, participants in the lowest (<= 1.4 mEq/L) category of serum Mg compared with the highest (>= 1.8 mEq/L) ones were at higher PAD risk (HR: 1.3; 95% confidence interval (CI): 1.06-1.58) (p value = 0.004). The HRs for PAD in 1.5, 1.6 and 1.7 mEq/L of serum Mg were 1.29 (95% CI: 1.08-1.54), 1.05 (95% CI: 0.89-1.24), and 1.0 (95% CI: 0.85-1.18), respectively. Conclusions: Low serum Mg was independently associated with an increased prevalence of PAD in the large population-based study; further studies are needed to confirm our findings.