CD33 or Siglec-3 (sialic acid-binding Ig-like lectin 3, SIGLEC3, SIGLEC-3, gp67, p67) is a transmembrane receptor expressed on cells of myeloid lineage.

It is usually considered myeloid-specific, but it can also be found on some lymphoid cells.

It binds sialic acids, therefore it is a member of the SIGLEC family of lectins.