Increased carotid intima–media thickness (cIMT) and stiffness, reflecting subclinical atherosclerosis, are associated with obstructive sleep apnea syndrome (OSAS). The relationship between serum fetuin-A, which inhibits ectopic calcification, and atherosclerosis is unclear. Therefore, we investigated the association between serum fetuin-A levels and carotid artery stiffness and cIMT in patients with normotensive OSAS (n = 50) and non-OSAS controls (n = 38). Compared with controls, there were lower fetuin-A levels (59.4 ± 6.5 vs 68.2 ± 5.8 ng/mL, P = .029), higher mean cIMT (0.73 ± 0.2 vs 0.63 ± 0.3 mm, P < .001), and greater stiffness (β) index (7.45 ± 0.9 vs 5.2 ± 0.7, P = .001) in the OSAS group. The cIMT and stiffness (β) index were inversely correlated with fetuin-A levels (r = –.324, P = .033; r = –.466, P < .001, respectively) and positively correlated with apnea hypopnea index (r = .498, P < .001; r = .422, P = .001, respectively) in the OSAS group. Decreased serum fetuin-A levels were associated with subclinical carotid atherosclerosis in patients with normotensive OSAS.