Objective:To study the gene mutations of homeobox transcription factor(CSX/NKX2.5) associated with a Chinese family with secundum atrial septal defect(ASD). Methods:Polymerase chain reaction and DNA sequencing were used to check all the members in the family with ASD, and single strand conformation polymorphism analysis(SSCP) was used to check 126 normal control people for detecting the mutations of CSX/NKX2.5 gene. Results: Three mutations,G270A(Glu32Lys),G378A(Glu68Lys)andG390A(Glu72Lys)were identified in CSX/NKX2.5 gene of ASD patients. However, the other members in the family with ASD and the control did not have such gene mutations. Conclusion:These mutations of CSX/NKX2.5 gene, which were identified in a Chinese family, may be one of the secundum ASD etiologic causes.