CDKN1C and KCNQ1OT1 are imprinted genes that might be potential regulators of placental development. This study investigated placental expressions of CDKN1C and KCNQ1OT1 in monozygotic twins with and without selective intrauterine growth restriction (sIUGR). Seventeen sIUGR and fifteen normal monozygotic(MZ) twin pairs were examined. Placental mRNA expressions of CDKN1C and KCNQ1OT1 were detected by real-time fluorescent quantitative PCR. CDKN1C protein expression was detected by immunohistochemical assay and Western-blotting. In the sIUGR group, smaller fetuses had a smaller share of the placenta, and CDKN1C protein expression was significantly increased while KCNQ1OT1 mRNA expression was significantly decreased. The CDKN1C/KCNQ1OT1 mRNA ratio was lower in the larger fetus than in the smaller fetus (p < .05). In the control group, CDKN1C protein expression showed no difference between larger and smaller fetuses, while KCNQ1OT1 mRNA expression was significantly lower in the larger fetus, and the CDKN1C/KCNQ1OT1 mRNA ratio was higher in the larger fetus than in the smaller fetus (p < .05). Our findings showed that pathogenesis of sIUGR may be related to the co-effect of the up-regulated protein expression of CDKN1C and down-regulated mRNA expression of KCNQ1OT1 in the placenta.