To establish a method of iduronate-2-sulfatase (IDS) activity assay and mutation analysis of IDS gene for the prenatal diagnosis of mucopolysaccharidosis type II (MPSII).Prenatal diagnosis of two cases was performed using cultured fetal amniotic fluid cells. Enzyme activity of IDS in cultured fetal amniotic fluid cells extracted from the two pregnant women at high risk of MPS II was measured. Meanwhile, genomic DNA was extracted for fetal gender testing and mutation analysis of the IDS gene.Enzyme activity assay showed that IDS activity in amniotic fluid cells was significantly decreased. IDS gene sequencing showed that the male fetus was hemizygous mutant, and the female fetus was carrier of heterozygous mutation. Therefore the male fetus was an MPS II patient and the female fetus was a mutation carrier.Determination of IDS activity in fetal amniotic fluid cells together with IDS gene mutation analysis is a rapid, sensitive and accurate method of prenatal diagnosis of MPS II. Using this method, prenatal diagnosis for pregnant women at high risk of MPSII can be achieved.