Abstract Objective: We aimed to preliminarily assess whether low-dose aspirin（LDA）is beneficial in preventing preeclampsia in twin pregnancies. Design: An observational cohort study. Setting: Two hospital centers in Chongqing, China. Population: 932 twin-pregnant women. Methods: Among 932 participants, 277 in the First Affiliated Hospital of Chongqing Medical University were routinely treated with aspirin (100mg daily) from 12-16 weeks to 35 weeks of gestational age, while 655 in Chongqing Health Center for Women and Children were not taking aspirin during the whole pregnancy. We followed each subject and the individual details were recorded. Main Outcome Measures: The main outcome was to compare the incidence of preeclampsia in women with or without aspirin intaking. Results: LDA significantly reduced the risk of PE (OR: 0.48, 95% CI: 0.24-0.95, p=0.048) and ＜34 weeks preterm birth (OR: 0.50, 95% CI: 0.29-0.86, p=0.013), but showed possible benefits to lower the rate of SGA babies (OR: 0.74, 95% CI: 0.55-1.00, p=0.063). Moreover, the risk of postpartum hemorrhage was not increased by LDA (OR: 0.89, 95% CI: 0.35-2.26, p=1.000). Conclusions: Treatment with low-dose aspirin in women pregnant with twins could offer some protection against adverse pregnancy outcomes in the absence of any significantly increased risk of postpartum hemorrhage. Funding: The National Key Research and Development Program of China (2018YFC1002900), and National Natural Science Foundation of China (81520108013, 81771613, 81671488, 81871189). Keywords: Twin pregnancy, low-dose aspirin, preeclampsia, preterm birth, small for gestational age