While Slicer activity of Argonaute is central to RNAi, conserved roles of slicing in endogenous regulatory biology are less clear, especially in mammals. Biogenesis of erythroid Dicer-independent mir-451 involves Ago2 catalysis, but mir-451-KO mice do not phenocopy Ago2 catalytic-dead (Ago2-CD) mice, suggesting other needs for slicing. Here, we reveal mir-486 as another dominant erythroid miRNA with atypical biogenesis. While it is Dicer dependent, it requires slicing to eliminate its star strand. Thus, in Ago2-CD conditions, miR-486-5p is functionally inactive due to duplex arrest. Genome-wide analyses reveal miR-486 and miR-451 as the major slicing-dependent miRNAs in the hematopoietic system. Moreover, mir-486-KO mice exhibit erythroid defects, and double knockout of mir-486/451 phenocopies the cell-autonomous effects of Ago2-CD in the hematopoietic system. Finally, we observe that Ago2 is the dominant-expressed Argonaute in maturing erythroblasts, reflecting a specialized environment for processing slicing-dependent miRNAs. Overall, the mammalian hematopoietic system has evolved multiple conserved requirements for Slicer-dependent miRNA biogenesis. Display omitted •Conserved, erythroid miR-486 requires slicing of its passenger strand by Ago2•miR-486/451 are the dominant slicing-dependent miRNAs in the hematopoietic compartment•Their loss together explains the erythroid phenotype of Ago2 slicing-deficient mice•Erythroid tissue has conserved signature of Ago2-only expression in mouse and human Jee et al. reveal that a major conserved rationale for mammalian Argonaute2 slicing is for the combined maturation of miR-486 and miR-451, miRNAs necessary for erythroid development. Their loss phenocopies the erythroid defects of slicing-deficient mice, and this slicing requirement explains the unique Ago2-only expression pattern found in erythroid tissue.