Background/aim: Vitamin D levels have been investigated in children with familial Mediterranean fever (FMF), but the relationship between vitamin D status and inflammation/oxidative stress indicators could not be clearly demonstrated. This study aimed to investigate the relationship between subclinical inflammation/oxidative stress and vitamin D status in children with FMF during an attack-free period. Materials and methods: In the cross-sectional study, ninety children with FMF in the attack-free period and 30 healthy children were included. Patients were grouped according to their vitamin D status (< 20, 20–29, and 30–100 ng/mL). The groups were compared in terms of pentraxin 3 (PTX-3), total oxidant status (TOS), and total antioxidant status (TAS). Multivariable linear regression analysis was performed to identify factors associated with vitamin D status. Results: PTX-3 levels were significantly higher in patients with vitamin D insufficiency (20-29 ng/mL) than in the group with vitamin D sufficient (30–100 ng/mL). Patients with vitamin D deficiency (< 20 ng/mL) had higher TOS. A strong negative correlation was observed between vitamin D levels and TOS (p = 0.003). Subclinical inflammation (PTX-3 ≥ 0.640) and high TOS levels were negatively associated with vitamin D levels. Conclusion: Subclinical inflammation and oxidative stress were negatively associated with vitamin D levels in patients with FMF during an attack-free period. Sufficient vitamin D levels are important in fighting subclinical inflammation and oxidative stress in children with FMF.