BCL11 genes play crucial roles in lymphopoiesis and have been associated with hematopoietic malignancies. Specifically, disruption of the BCL11B (B-cell chronic lymphocytic leukemia/lymphoma 11B) locus is linked to T-cell acute lymphoblastic leukemia, and the loss of heterozygosity in mice results in T-cell lymphoma. BCL11 proteins are related C 2 H 2 zinc-finger transcription factors that act as transcriptional repressors. Here, we demonstrate the association of the endogenous BCL11B with the nucleosome remodeling and histone deacetylase (NuRD) complex, one of the major transcriptional corepressor complexes in mammalian cells. BCL11B complexes from T lymphocytes possess trichostatin A-sensitive histone deacetylase activity, confirming the functionality of the complexes. Analysis of the BCL11B–NuRD association demonstrated that BCL11B directly interacted with the metastasis-associated proteins MTA1 and MTA2 through the amino-terminal region. We provide evidence for the functional requirement of MTA1 in transcriptional repression mediated by BCL11B through the following:(1) overexpression of MTA1 enhanced the transcriptional repression mediated by BCL11B,(2) knockdown of MTA1 expression by small interfering RNA inhibited BCL11B transcriptional repression activity and (3) MTA1 was specifically recruited to a BCL11B targeted promoter. Taken together, these data support the hypothesis that the NuRD complex mediates transcriptional repression function of BCL11B.