We reported a case of monochorionic monoamniotic twins discordant for anencephaly diagnosed by second-trimester ultrasonography at the First Affiliated Hospital of Fujian Medical University.Ultrasound at seven weeks of gestation showed only one gestational sac with an embryo inside.Another 12 gestational weeks' ultrasound scan performed at another hospital found one gestational sac and one fetus (crown-rump length was 6.11 cm and nuchal translucency was 0.11 cm) in the upper-middle uterine cavity.The ultrasound examination at 22+6 gestational weeks identified one placenta and two fetuses without obvious diaphragm echo in between.Although no structural abnormality was observed in one fetus,frog-like eyes,absence of skull image and brain tissue echo were presented in the other fetus.The patient was transferred to a higher level hospital and was successfully performed radiofrequency ablation for selective reduction at 23+4 weeks of gestation.At 35 weeks,a premature live boy and an anencephalic stillbirth fetus were born vaginally after premature rupture of membranes.The baby boy was healthy at follow-up at four months old.