In this study, we explored whether phloroglucinol (1,3,5-trihydroxybenzene) exerts protective effects against oxidative stress–induced cytotoxicity in SH-SY5Y cells, a neuroblastoma cell line. The central nervous system is especially vulnerable to oxidative stress because the brain consumes large amounts of energy to perform its complicated functions, but contains a lower level of anti-oxidant enzymes compared with other peripheral tissues. In SH-SY5Y cultures, pretreatment with 10 μg/ml of phloroglucinol attenuates the cytotoxicity of hydrogen peroxide. In addition, when assessed with 2′,7′-dichlorofluorescein diacetate dye, the increase in reactive oxygen species (ROS) induced by hydrogen peroxide was significantly reduced by pretreatment with phloroglucinol. ROS is known to cause lipid peroxidation of the cell membranes, the carbonylation of intracellular proteins, and DNA damage, which can lead to various cellular dysfunctions and eventually cellular death. We found that pretreatment with phloroglucinol down-regulated the levels of 8-isoprostane, protein carbonylation, and 8-hydroxy deoxyguanine caused by hydrogen peroxide treatment in SH-SY5Y cells. These results indicate that phloroglucinol exerts protective effects against oxidative stress-induced cell damage in SH-SY5Y cells.