© 2022 American Society for Pain Management NursingBackground: Fibromyalgia syndrome (FMS) is a chronic pain condition that requires multidisciplinary treatment. Vitamin K is an antioxidant that plays a role in many reactions in the body, and its effectiveness in FMS has not been studied before. Aim: We aimed to evaluate vitamin K levels in FMS patients and their relationship with pain, disease activity, quality of life, and inflammatory cytokines. Method: Eighty-eight female patients with FMS and 87 controls were included in the study. Vitamin K and inflammatory cytokine (interleukin-6 [IL-6], IL-8, tumor necrosis factor [TNF]-alfa) serum levels were measured in both groups. Visual Analog Scale (VAS), Fibromyalgia Impact Questionnaire (FIQ), and Short Form-36 (SF-36) scales were used. Results: No statistically significant differences in vitamin K levels between the two groups, and no relationships were found between these levels and pain, FIQ, SF-36, and inflammatory cytokines (p > .05). While IL-6 and TNF-alpha levels were found to be high in the FMS group compared with the control group (p < .05), no difference in IL-8 levels was noted (p > .05). In the FMS group, positive correlations were found between IL-6 and FIQ, and between TNF-alpha and physical role difficulty(p > .05). Conclusions: Overall, the results of this study do not provide any evidence of an association between FMS and vitamin K levels. However, high IL-6 and TNF-alpha levels suggest that low-intensity inflammation may accompany FMS and have a negative impact on physical activity. Future studies are needed to determine the relationship between vitamin K and FMS.