Paraoxonase-1 (PON1) is an HDL-bound enzyme system which plays a key role in the protection of LDL and HDL from oxidation by hydrolysing activated phospholipids and lipid peroxide products. Oxidative stress has been involved in the pathogenesis of many complications of human pregnancy, including early pregnancy failure (EPF), preeclampsia and preterm labour. The purpose of this study was to determine serum paraoxonase/arylesterase activities and lipid hydroperoxide (LOOH) levels as an oxidative stress indicator in women with EPF.Paraoxonase/arylesterase activities and LOOH levels were assessed in women with EPF (n = 40) and healthy continuum pregnant women without EPF (n = 38) before 12 weeks' gestation. Serum basal and salt-stimulated paraoxonase/arylesterase activities were measured spectrophotometrically. LOOH levels were measured by ferrous oxidation with a xylenol orange assay. Student's t-test and the Pearson correlation were used for statistical analysis.We found that basal and salt-stimulated paraoxonase/arylesterase activities were significantly lower in women with EPF than in women without EPF (all p <0.05), while LOOH levels were significantly higher (p = 0.009).Our study showed that decreased paraoxonase/arylesterase activities and increased LOOH levels may play a role in ethiopathogenesis through increased susceptibility to lipid peroxidation in women with EPF.