Translocations of regulator proteins from or to the mitochondria are key events in apoptosis regulation. NOA36/ZNF330 is a highly evolutionary conserved protein with a characteristic cystein-rich domain. In this work we address its mitochondrial localization and we demonstrate that a blockage of endogenous NOA36/ZNF330 expression by small-interfering RNA (siRNA) reduced apoptotic response to etoposide (ETO), camptothecin (CPT) and staurosporine (STS) but not to CH11 anti-Fas antibody or tumour-necrosis-factor-related apoptosis-inducing ligand (TRAIL) in HeLa cells. In contrast, when ectopically expressed in the cytoplasm, NOA36/ZNF330 induces apoptotic cell death. We also found that the domain responsible for this proapoptotic activity is located its cystein-rich region. We propose that NOA36/ZNF330 is translocated from the mitochondria to the cytoplasm when apoptosis is induced and that it contributes to cytochrome c release.