Aim: To compare the levels of serum prolidase activity and oxidative stress markers, including total oxidative status (TOS), total antioxidant capacity (TAC), oxidative stress index (OSI), and total free sulfhydryl (-SH) in healthy pregnant women and pregnant women with intrauterine growth restricted infants. Methods: Serum samples were obtained from 18 healthy third trimester pregnancies and 14 pregnancies complicated by fetal growth restriction (FGR). The criteria for FGR were clinical evidence of suboptimal growth, ultrasonographic demonstration of deviation from normal percentiles of growth, and birthweight under the 10th percentile. We spectrophotometrically measured serum prolidase activity, TAC, TOS, and -SH levels. Oxidative stress was determined from total antioxidant capacity and total oxidant status measurement and calculation of the oxidative stress index. Results: Serum TAC and -SH levels were significantly lower in the FGR group than in the healthy control group (P = 0.001, P < 0.001, respectively), whereas TOS level, OSI value, and prolidase activity were significantly higher (P = 0.003, P < 0.001, P < 0.001, respectively). Prolidase activity was positively correlated with TOS and OSI values (rho = 0.552, P = 0.041 and rho = 0.635, P = 0.015, respectively) and negatively correlated with TAC and -SH levels (rho = -0.578, P = 0.030 and rho = -0.622, P = 0.018, respectively). Conclusion: The present study shows that serum prolidase activity and oxidative stress are significantly associated with the presence of FGR and that the correlation between serum prolidase activity and markers of oxidative stress are represented as increased serum TOS level and decreased serum TAC and -SH levels, suggesting an association of collagen turnover and oxidative stress in vascular dysfunction. © 2009 Japan Society of Obstetrics and Gynecology.