Acute and chronic abuses of psychostimulant drugs such as methamphetamine (METH) have been known to cause cell death. In particular, neurotoxicity caused by such drugs is one of the most serious adverse events in humans. Although various effects on neuronal cells caused by METH have been studied, the cellular and molecular mechanisms of METH-induced neurotoxicity remain to be elucidated. To investigate the mechanism of METH-induced cytotoxicity, we studied cytological as well as biochemical changes in retinoic acid (RA)-differentiated SH-SY5Y human neuroblastoma cells. Marked cell death was observed with more than 7mM METH, although caspase-dependent apoptotic cell death was not observed with any concentration of METH treatment. The most prominent cytomorphological effect by METH was the formation of large cytoplasmic vacuoles which were not colocalized with either GFP-LC3 or HSP47-GFP, autophagosome and ER markers respectively. In contrast, many of these vacuoles incorporated large molecular weight FITC-dextran and were confirmed as macropinosomes. Our results indicate that METH-induced cytomorphological effects on RA-differentiated SH-SY5Y human neuroblastoma cells involve macropinocytosis and the hyperstimulation of this process may be involved in METH-caused cytotoxicity.