Objective To detect the development of fetal nasal bone with ultrasound scan in the second and third trimester, and to evaluate the value of fetal nasal bone hypoplasia in diagnosing fetal chromosomal abnormalities. Methods Prenatal ultrasound examination was performed in 1415 normal fetuses. The nasal bone length (NBL) and the nasal bone angle (NBA) were measured on the mid-sagittal plane. The karyotype of the cases with nasal bone abnormality was analyzed. Results The fetal nasal bone was successfully detected with two-dimensional ultrasonography in 95% of the subjects. The NBL increased with the gestational age while the NBA kept unchanged with the average value of 54. 4?(44. 4?-69. 2?). Forty-two cases with nasal bone hypoplasia were diagnosed prenatally including nasal bone defect (20 cases), small NBA (15 cases), short nasal bone (4 cases) and short nasal bone with small NBA (3 cases). Cordocentesis was performed in 21 cases among which 12 with abnormal karyotype, including 3 cases of trisomy 21, 3 cases of trisomy 13, 4 cases of trisomy 18 and 3 other chromosomal abnormalities. Conclusions Fetal nasal bone hypoplasia was closely related to the chromosomal abnormalities. The evaluation of fetal nasal bone with prenatal sonography is an important criteria for screening fetal chromosome abnormalities during the mid-trimester.