Abstract The origin of dendritic cells (DCs) in tumors remains obscure. Recent studies indicate that conventional DCs (cDCs) in lymphoid tissues arise from a distinct population of committed cDC precursors (pre-cDCs) that originate in bone marrow and migrate via blood. In this study, we show that pre-cDCs are precursors for cDCs in tumors. Pre-cDCs from tumors, bone marrow, and spleen exhibit similar morphologic, immunophenotypic, and functional properties. Adoptive transfer studies show that bone marrow pre-cDCs migrate from blood into the tumor where they generate cDCs. The chemokine CCL3, which is markedly upregulated in tumors, promotes pre-cDC recruitment. Both pre-cDCs and their cDC progeny actively proliferate within the tumor. cDCs that arise from pre-cDCs in tumors express lower levels of CD11c and MHC class II as compared with those in spleen; however, there was no difference in their abilities to respond to maturation stimuli or activate Ag-specific lymphocytes in vitro. Our study provides the first evidence supporting a role for pre-cDCs in DC development in tumors and suggests a potential target for cancer immunotherapy.