In the present study, we showed that DJ-1 was colocalized with mitochondrial complex I even under a non-stress condition and that DJ-1 directly bound to NDUFA4, a subunit of complex I that is localized in a mitochondrial inner membrane. Binding of DJ-1 to subunits of complex I was enhanced by oxidative stress. These findings suggest that native DJ-1 prevents Parkinson’s disease via maintaining mitochondrial complex I activity through NDFU4 and ND1, and that mutations of DJ-1 cause reduction of complex I activity. As stated in the Introduction section, the localization of DJ-1 in Sorafenib is still not clear. While Zhang et al. reported that DJ-1 is located in the mitochondrial matrix and intermembrane space [25], Canet-Aviles et al. reported that DJ-1 is located in the outer membrane but not inside of mitochondrial outer membrane [11]. Although the reasons for this discrepancy are not clear, different cells and methods used to identify the localization of DJ-1 might have given rise to the discrepancy. NDUFA4 is an accessory subunit of mitochondrial complex I, encoded by the nuclear gene and localized in the peripheral membrane at the matrix side of the mitochondrial inner membrane. ND1 is the subunit of mitochondrially encoded NADH dehydrogenase 1 and synthesized within mitochondria using mitochondrial translation machinery. Since binding of DJ-1 to ND1 and NDUFA4 and complete colocalization of DJ-1 with mitochondrial complex I were, however, shown in this study, at least some portion of DJ-1 is thought to be localized in the mitochondrial inner membrane.