Astrocytes constitute about 20-40% of glial cells, making up the central nervous system (CNS). In the CNS, astrocytes supply neurons with nutritional factors and maintain homeostasis of the extracellular environment through the uptake and efflux of neurotransmitters. In neurodegenerative diseases, astrocytes change their morphology to the activated state and release inflammatory cytokines, which induce CNS inflammation and aggravate neurodegenerative diseases. Sphingolipids, one of the lipids, have been reported as a molecule associated with astrocyte activation, but their involvement remains unclear. In this study, we evaluated astrocyte activity by changing the levels of sphingomyelin (SM), one of the most abundant sphingolipids, using human astrocyte/conditionally immortalized clone 35 (HASTR/ci35). Reduction of SM levels by knockdown of sphingomyelin synthase 1 and/or 2 in HASTR/ci35 attenuated HASTR/ci35 activation by treatment of inflammatory cytokines. Furthermore, selectively reducing SM levels by knockdown of ceramide transport protein also attenuated the activation of HASTR/ci35. On the other hand, increasing the levels of SM by inhibition of neutral sphingomyelinase or addition of SM exogenously promoted activation of HASTR/ci35 by treatment of inflammatory cytokines. These results suggest that SM positively regulates astrocyte activation. Thus, regulating SM levels may provide a therapeutic target for astrocyte-induced CNS inflammation and a new approach to treating neurodegenerative diseases.