Objective: To evaluate the maternal serum levels of sFlt-1, PlGF and sFlt-1/PlGF ratio in suspected preeclampsia patients with twin pregnancies compared to singleton pregnancies. Methods: This was a retrospectively study on women who had received the laboratory tests including maternal serum levels of sFlt-1, PlGF and sFlt-1/PlGF ratio for the purpose of evaluation for preeclampsia at Seoul National University Bundang Hospital between March 2019 and June 2020. Two triplet pregnancies were excluded. A total of 104 singleton pregnancies and 35 twin pregnancies were included and divided into groups according to the diagnosis of preeclampsia. Obstetric and neonatal outcomes were compared in the groups classified by the well-known cut-off of the sFlt-1/PlGF ratio: below 38, 38-85, and over 85 in singletons and twins, respectively. Results: Among the study population, 35% (49/139) were diagnosed as preeclampsia (38/66 in singleton pregnancies and 11/35 in twin pregnancies). The levels of sFlt-1 and PlGF were significantly different between twins and singletons when analyzed both in the group without and with preeclampsia (p-values, all < 0.05). However, the sFlt-1/PlGF ratio were comparable between twins and singletons in the group without and with preeclampsia. The rates of preterm birth before 34 weeks of gestation were significantly different according to the cut-offs of the sFlt-1PlGF ratio in singletons (2.8% in below 38 vs. 12.5% in 38-85 vs. 43.8% in over 85, p<0.001), however the difference did not reach statistical significance in twin pregnancies. Conclusion: Unlike the sole level of sFlt-1 or PlGF, the sFlt-1/PlGF ratio in twin pregnancies with preeclampsia is not different from that in singletons. Nevertheless, the predictive value of the sFlt-1/PlGF for the adverse outcomes of preeclampsia seems to be better in singletons than twins.