Chicken Annexin V (also known as ANXA5, Annexin A5, placental anticoagulant protein I (PAP-I), lipocortin V, or anchorin CII) is a calcium-dependent phospholipid-binding protein belonging to the annexin family, which is involved in membrane organization, cellular signaling, and regulation of inflammation and apoptosis. In chickens (Gallus gallus), Annexin V binds with high affinity to phosphatidylserine that becomes exposed on the outer leaflet of the plasma membrane during early apoptosis or cellular stress in the presence of calcium ions. Because of this property, FITC-labeled chicken Annexin V (Annexin V–FITC) is widely used in flow cytometry and fluorescence microscopy assays to detect apoptotic cells. The fluorescein isothiocyanate (FITC) conjugation enables fluorescent labeling of cells exposing phosphatidylserine, allowing sensitive quantification of early apoptotic cells, often in combination with viability dyes such as propidium iodide (PI) to distinguish early apoptosis from late apoptosis or necrosis. In avian health and research, Annexin V–FITC assays are used to investigate cellular responses during viral infections such as avian influenza virus, Newcastle disease virus, and Marek’s disease virus, as well as bacterial infections and immune-mediated tissue damage. It is also used in studies of embryonic development, immune cell viability, and reproductive biology in poultry. As a biomarker of apoptosis and membrane remodeling, chicken Annexin V supports research into host–pathogen interactions, immune regulation, vaccine responses, and cell death pathways relevant to avian biology and poultry health.