The objective of this study was to investigate the relationship between serum total thiol level and total oxidant status (TOS) and thrombocytopenia among patients with Crimean-Congo hemorrhagic fever (CCHF). Eighty-three subjects and 56 controls were enrolled in the study. Thiol levels were measured with the DTNB method and TOS was measured with the Erel's method among subjects and controls. Thiol levels were lower in subjects than controls and TOS levels were higher in subjects than controls. There was a significant correlation between total thiol levels and platelet counts (r=0.84, p<0.0001) among subjects. Further investigations are needed into the link between total thiol level and TOS and the pathogenesis of hemorrhage in CCHF.