Objective: To determine whether a mutation of mitochondrial DNA induces familial dilated cardiomyopathy in Chinese families with cardiomyopathy, and analyzed the correlation between the genotype and phenotype. Methods: Affected members in three Chinese families of the familial dilated cardiomyopathy underwent clinical evaluation and DNA analysis. Polymerase chain reaction and direct DNA sequencing were used to screen for mitochondrial DNA mutation. The type of mtDNA vairations and clinical situation were analysed on the patients with mitochondrial DNA mutation. Results: The mitochondrial A3434G mutation was identified in one of the three families,the 3434 th nucleotide A was replaced by G, which led to change of amino acid. No mutations were identified in the clinically unaffected members of the family and all members of the other two families.Conclusion: This study indicates that the mitochondrial A3434G mutation maybe related with familial dilated cardiomyopathy and deafness.