The control of self-renewal and differentiation of neural stem and progenitor cells is a crucial issue in stem cell and cancer biology.Drosophila neural stem cell, larval brain neuroblast, has recently emerged as a model for the study of stem cell self-renewal and tumor formation.Drosophila type II neuroblast lineages are prone to developing impaired neuroblast homeostasis if the limited self-renewing potential of intermediate neural progenitors (INPs) is unrestrained.Here, we demonstrate that Drosophila SWI/SNF chromatin remodeling Brahma (Brm) complex functions cooperatively with another chromatin remodeling factor, Histone deacetylase 3 (HDAC3) to suppress the formation of ectopic neural stem cells.We show that multiple components of the Brm complex and HDAC3 physically associate with Earmuff (Erm), a type Ⅱ-specific transcription factor that prevents dedifferentiation of INPs into neural stem cells.Consistently, the predicted Erm-binding motif is present in most of known binding loci of Brm.Furthermore, brm and hdac3 genetically interact with erm to prevent neural stem cell overgrowth.Thus, the Brm-HDAC3-Erm repressor complex suppresses dedifferentiation of INPs back into neural stem cells.