Intracellular factors are involved in and essential for hematopoiesis. HIV-1 Tat-interacting protein of 110 kDa (TIP110; p110(nrb)/SART3/p110) is an RNA-binding nuclear protein implicated in the regulation of HIV-1 gene and host gene transcription, pre-mRNA splicing, and cancer immunology. In the present study, we demonstrate a role for TIP110 in the regulation of hematopoiesis. TIP110 was expressed in human CD34(+) cells and decreased with differentiation of CD34(+) cells. TIP110 mRNA was also expressed in phenotyped mouse marrow hematopoietic stem cells (HSCs) and hematopoietic progenitor cells (HPCs). Using TIP110 transgenic (TIP110(TG)) and haploinsufficient (TIP110(+/-)) mice, we found that increased TIP110 expression enhanced HPC numbers, survival, and cell cycling, whereas decreased TIP110 expression had the opposite effects. Moreover, TIP110(+/-) bone marrow HPCs responded more effectively, and TIP110(TG) HPCs less effectively, than those of wild-type control mice to recovery from the cell-cycle-active drug 5-fluorouracil (5-FU). Unexplained sex differences were noted in HSC competitive repopulating ability, but not HPC numbers, in TIP110(TG) mice. Intracellularly, TIP110 regulated CMYC and GATA2 expression at the transcriptional level, and TIP110 and CMYC reciprocally regulated the expression of each other. These results demonstrate a role for TIP110 in the regulation of hematopoiesis, effects that are likely linked to TIP110 regulation of CMYC.