A widely-used plasticizer di(2-ethylhexyl) phthalate (DEHP) is known to induce apoptosis in neurons, although the mechanisms responsible for DEHP-induced apoptosis is not well explored yet. We recently showed that exposure to DEHP increases the expression of hemeoxygenase (HO)-1, an oxidative stress related enzyme, in the mice brain. In this study, we investigated whether HO-1 is involved in DEHP-induced apoptosis using a mouse neuroblastoma cell line Neuro-2a, which forcibly express SCAT3, a fluorescent indicator of caspase-3 activity. The doses of DEHP at 1, 10 or 100 µM were used in the present study to mimic the level of human exposure to DEHP. Live image analysis of SCAT3-expressing Neuro-2a cells revealed that caspase-3 activity in the cells was significantly increased by DEHP at 100 µM but not 1 or 10 µM. We measured HO-1 mRNA level in Neuro-2a cells exposed to DEHP and found significant increase in HO-1 mRNA level by DEHP at 100 µM but not 1 or 10 µM. Live image analysis of SCAT3-expresisng Neuro-2a cells was further performed to determine the effects of HO-1 siRNA in DEHP-induced apoptosis via caspase-3 activation. We found that knockdown of HO-1 gene nullifies the effects of DEHP to activate caspase-3. These results suggest that HO-1 is involved in DEHP-induced apoptosis. Moreover, this study demonstrates that high-dose DEHP exposure induces caspase-3-dependent apoptosis, which is at least partially mediated by the up-regulation of HO-1 gene, in Neuro-2a cells.