Mitochondrial dysfunction may cause diabetes or insulin resistance. Peroxisome proliferation-activated receptor-gamma (PPAR-gamma) coactivator-1 alpha (PGC-1alpha) increases mitochondrial transcription factor A (Tfam) resulting in mitochondrial DNA content increase. An association between a single nucleotide polymorphism (SNP), G1444A(Gly482Ser), of PGC-1alpha coding region and insulin resistance has been reported in some ethnic groups. In this study, we investigated whether a change of glycine to serine at codon 482 of PGC-1alpha affected the Tfam promoter activity. The cDNA of PGC-1alpha variant bearing either glycine or serine at 482 codon was transfected into Chang human hepatocyte cells. The PGC-1alpha protein bearing glycine had impaired coactivator activity on Tfam promoter-mediated luciferase. We analyzed the PGC-1alpha genotype G1444A and mitochondrial DNA (mtDNA) copy number from 229 Korean leukocyte genomic DNAs. Subjects with Gly/Gly had a 20% lower amount of peripheral blood mtDNA than did subjects with Gly/Ser and Ser/Ser (p<0.05). No correlation was observed between diabetic parameters and PGC-1alpha genotypes in Koreans. These results suggest that PGC-1alpha variants with Gly/Gly at 482nd amino acid may impair the Tfam transcription, a regulatory function of mitochondrial biogenesis, resulting in dysfunctional mtDNA replication.