To identify a cisplatin resistance predictor to reduce or prevent unnecessary side effects, we firstly established four cisplatin-resistant sub-lines and compared their protein profiles with cisplatin-sensitive parent lung cancer cell lines using two-dimensional gel electrophoresis. Between the cisplatin-resistant and -sensitive cells, a total of 359 protein spots were differently expressed (>1.5 fold), and 217 proteins (83.0%) were identified. We focused on a mitochondrial protein, hydroxyl-coenzyme A dehydrogenase/3-ketoacyl-coenzyme A thiolase/enoyl-coenzyme A hydratase alpha subunit (HADHA), which was increased in all cisplatin-resistant cells. Furthermore, pre- treated biopsy specimens taken from patients who showed resistance to platinum-based treatment showed a significantly higher positive rate for HADHA in all cases (p=0.00367), including non-small cell lung carcinomas (p=0.002), small-cell lung carcinomas (p=0.038), and adenocarcinomas (p=0.008). These results suggest that the expression of HADHA may be a useful marker to predict resistance to platinum-based chemotherapy in patients with lung cancer.