Glioblastoma multiforme (GBM) is the most aggressive primary brain cancer in adults. Current treatments prove ineffective in prolonging patient survival beyond 15 months. Molecular characterization of GBM tumors suggest that a minor fraction, called brain tumor stem cells (BTSC), initiate and maintain the tumor; while the majority of cells that resembles differentiated astrocytes are unable to do so. Thus, differentiating the BTSCs may be used as supplementary therapy for GBM. In this regard, a recent study showed that cMyc (hereafter referred to as Myc, in accordance with new nomenclature) expression in differentiated murine astrocytes renders them tumorigenic. Conversely, activated Stat3 is involved in differentiation of murine neural stem cells into astrocytes. However, the mechanisms underlying human GBM cell differentiation are unknown. So we hypothesized that Myc is associated with GBM tumorigenesis, and its interplay with activated Stat3, modulates GBM cell differentiation thereby affecting tumor formation. To test this hypothesis we pursued three specific aims. First, the level of Myc protein was monitored in human GBM cells to determine any correlation between Myc and tumorigenicity of the cells. Secondly, the relationship between Myc and activated Stat3 was explored to determine if a regulatory mechanism exists between these two transcription factors. Finally, the mechanism of Myc-mediated suppression of glial fibrillary acidic protein (GFAP), a differentiation marker, was investigated. Our results demonstrated that the tumorigenic GBM cell line U87, had higher steady state level of Myc than that in a less tumorigenic GBM cell line, U251. Importantly, activated Stat3 suppressed the steady state level of Myc and thus affected Myc-regulated targets and function in GBM cells. GFAP expression was associated with differentiated astrocytes, and Myc suppresses GFAP expression by an unknown mechanism. Here, we show that Myc inhibited the GFAP promoter activation in human GBM cells. Collectively, these results support our hypothesis that Myc is positively associated with GBM tumorigenicity, and activated Stat3 suppresses Myc protein that inhibits GFAP promoter activation.