Alemtuzumab is a humanized recombinant monoclonal antibody that specifically targets the CD52 antigen, which is expressed on both malignant and normal T and B lymphocytes. By binding to CD52, alemtuzumab exerts potent antitumor and immunosuppressive effects. Initially approved by the FDA in 2001 for the treatment of B-cell chronic lymphocytic leukemia (B-CLL), alemtuzumab's therapeutic applications have expanded to various hematologic malignancies, including lymphoma, acute leukemia, myelodysplastic syndromes (MDS), aplastic anemia (AA), graft-versus-host disease (GVHD), and chimeric antigen receptor T-cell (CAR-T) therapy. This review evaluates the efficacy and safety of alemtuzumab in these conditions, aiming to synthesize current evidence and provide guidance for clinical practice to optimize the use of alemtuzumab in the treatment of these diseases.