Abstract: To explore the mechanism of TBX5 abnormal expression in simple congenital heart disease (CHD), 100 CHD venous blood, 50 CHD heart tissues, and 5 non-CHD heart tissues were involved in this study. The mutation and methyla-tion in the 1 200 bp region upstream of TBX5 gene were detected by high-performance liquid chromatography (DHPLC) and methylation-sensitive restriction endonuclease (MS-RE), respectively. The binding site of NKX2-5 to Tbx5 predicted by P-MATCH software was validated by EMSA (Electrophoretic mobility shift assay). Tbx5 gene expression in mouse cardiac muscle cell H9C2(2-1) transfected with NKX2-5 expression vector was evaluated. No mutation was found in all patients. Both non-CHD and CHD heart tissues had the same methylation in the two CpG islands. Exogenous Nkx2-5 efficiently activated the transcription of the endogenous Tbx5 gene in H9C2 (2-1) cells. EMSA showed that the special binding band appeared when Nkx2-5 existed. These results indicates that the down expression of TBX5 might not be caused by mutation and methylation in the 1 200 bp region upstream of gene, and might be regulated by abnormal expression of NKX2-5 gene in heart muscle of CHD.