Objective: This study aimed to evaluate the differences in maternal renal function between singleton and twin pregnancies in the second half of pregnancy. Design: Retrospective study Setting: Japanese Red Cross Aichi Medical Center Nagoya Daiichi Hospital from January 2019 to June 2021. Population: This study included 1711 pregnant women with 1547 singleton pregnancies and 164 twin pregnancies. Methods: Patients underwent renal function tests (serum blood urea nitrogen, creatinine, and estimated glomerular filtration rate [eGFR]) at least one month prior to delivery. Main Outcome Measure: Maternal renal dysfunction, defined as serum creatinine of above 0.8 mg/dL. Results: Serum creatinine level was significantly higher and eGFR was significantly lower in twin pregnancies than that in singleton pregnancies (p < 0.001). In addition, the rate of renal dysfunction was significantly higher in twin than that in singleton pregnancies (7.9% vs. 2.6%; p < 0.001). Multivariate analysis revealed that twin pregnancy (odds ratio [OR] 3.38), nulliparity (OR 2.31), and preeclampsia (OR 3.64) were significant risk factors for maternal renal dysfunction. Maternal renal dysfunction was observed in 13 twin pregnancies, all of which recovered to within normal limits during the postpartum period. Conclusions: Twin pregnancy is a significant risk factor for maternal renal dysfunction. Careful attention should be paid to maternal renal dysfunction in the management of twin pregnancies. Funding: Japanese Red Cross, Nagoya Daiichi Hospital Research Grant (grant number NFRCH22-0011). Keywords: chorionicity, renal function, serum creatinine concentration, singleton pregnancy, twin pregnancy