Mitochondrial dysfunction is an important cause of neurological disorder including Alzheimer's disease (AD). Mitochondria play a key role in the generation of reactive oxygen species (ROS), resulting in oxidative damage to neuronal cell and cellular compartments in the AD brain. Cytotoxicity induced by amyloid-beta (Abeta), a protein fragment of 25-35 amino acids in amyloid plaques has been shown to have neuro-toxic properties. They seem to involve mitochondrial dysfunction, but the underlying mechanisms are not clearly understood. The purpose of this study was to assess whether Abeta induced mitochondrial dysfunction involves changes in cytochrome c oxidase (COX) expression. We measured the activities of COX after expose of SK-N-SH cells (a human neuroblastoma cell line) to Abeta. We found that levels of mRNAs expressing mitochondrial COX subunits decreased significantly in Abeta-treated SK-N-SH cells in a dose-dependent manner. Human mitochondrial transcription factor-1 (TFAM) mRNA level also decreased after Abeta-treatment. These results suggest that Abeta modulates the mitochondrial gene expression through a decrease in TFAM.