Objective-Sialic acid, a terminal component of glycoproteins and glycolipids, is found to be elevated in many pathologic conditions, including preterm deliveries and uterine dysfunction. Along with increased lipid peroxides, it is one of the indices of oxidative stress seen in recurrent abortion. This article investigates whether changes in plasma total sialic acid (TSA) and lipid-bound sialic acid (LSA) contribute to this condition. Patients and Methods-Plasma samples of 25 nonpregnant (NP) healthy women, 25 normotensive pregnant women (NTP), and 120 women with recurrent abortion (RA) were assayed for TSA, LSA, total protein (TP), and TSA/TP. Recurrent aborters were divided into four subgroups according to etiology: 25 autoimmune (AUTO), 25 luteal phase defect (LPD), 20 anatomical defect (AD), and 50 with unexplained etiology (UNEx). Results-Plasma TSA and LSA levels were significantly elevated in AUTO aborters in comparison with controls (NP and NTP) and other recurrent abortion subgroups. TSA/TP value was significantly increased in abortion with immunological and unexplained etiology (AUTO and UNEx). Conclusions-According to our results we can suggest that elevation of TSA and LSA is indeed a reflection of the immunologic abnormalities in the AUTO group, and that TSA and LSA increase is secondary to the underlying disease of AUTO aborters.