Thanatophoric dysplasia (TD) is a relatively common lethal skeletal dysplasia. These malformations result from the mutations in fibroblast growth factor receptor 3 (FGFR3) gene, which is located on the short arm of chromosome 4. Accurate diagnosis of fetal TD is important for patient counseling and to plan the management. A definite diagnosis can be established by molecular genetic analysis to find out the abnormal mutations in the FGFR3 gene. We reported on two cases of TD type I found by prenatal ultrasound and confirmed by molecular analysis of FGFR3 gene using high-resolution melting analysis.