The aim of this study was to the investigate the effect of brucellosis infection on paraoxonase-1 (PON1) activity and oxidative status in patients with brucellosis. Sixty patients with brucellosis (47 acute, 13 subacute) and the 67 healthy controls were used in the study. Serum PON1 and arylesterase activities, total antioxidant capacity (TAC), total oxidant status (TOS), oxidative stress index (OSI), total free sulfhydryl (-SH), and lipid hydroperoxide (LOOH) groups were determined. In addition, HDL-cholesterol (HDL-C), LDL-cholesterol (LDL-C), total cholesterol (TC) and triglyceride (TG) were measured. Serum PON1 and arylesterase activities, total -SH group levels and TAC were significantly lower in brucellosis patients than controls (P<0.001). TOS, OSI and LOOH levels were significantly higher in brucellosis patients than controls (P<0.001). There were no significant differences between of serum LDL-C, TG and TC levels of patients subjects compared to controls (P > 0.05). Patients with brucellosis are exposed to potent oxidative stress and they have decreased PON1 activity. These predisposal factors might play a role in the pathogenesis for atherosclerosis in patients with brucellosis.