Abstract The histone acetyltransferases (HATs) of the MYST family include TIP60, HBO1, MOZ/MORF, and MOF and function in multisubunit protein complexes. Bromodomain-containing protein 1 (BRD1), also known as BRPF2, has been considered a subunit of the MOZ/MORF H3 HAT complex based on analogy with BRPF1 and BRPF3. However, its physiologic function remains obscure. Here we show that BRD1 forms a novel HAT complex with HBO1 and regulates erythropoiesis. Brd1-deficient embryos showed severe anemia because of impaired fetal liver erythropoiesis. Biochemical analyses revealed that BRD1 bridges HBO1 and its activator protein, ING4. Genome-wide mapping in erythroblasts demonstrated that BRD1 and HBO1 largely colocalize in the genome and target key developmental regulator genes. Of note, levels of global acetylation of histone H3 at lysine 14 (H3K14) were profoundly decreased in Brd1-deficient erythroblasts and depletion of Hbo1 similarly affected H3K14 acetylation. Impaired erythropoiesis in the absence of Brd1 accompanied reduced expression of key erythroid regulator genes, including Gata1, and was partially restored by forced expression of Gata1. Our findings suggest that the Hbo1-Brd1 complex is the major H3K14 HAT required for transcriptional activation of erythroid developmental regulator genes.