Stem Cell Antigen-1 (Sca-1) is a member of the lymphocyte antigen 6 (Ly-6) family. It is expressed on multipotent hematopoietic stem cells (HSC) and is used as a marker of HSC in mice.

Sca-1 is used in combination with lineage depletion antibodies to identify murine HSC. Sca-1 can be found in fetal liver, adult bone marrow, and adult peripheral blood and spleen. Sca-1 may be involved in the regulation of B and T cell activation.