Antibodies against eosinophil cationic protein (ECP), a major granule protein of eosinophils, have been reported in a subset of patients with eosinophilic, allergic, and inflammatory disorders. ECP is a highly cationic ribonuclease released during eosinophil activation and degranulation and contributes to inflammatory tissue responses and host defense. Autoantibodies directed against ECP may reflect eosinophil activation, tissue injury, and alterations in immune tolerance. Elevated levels of anti-ECP antibodies have been investigated in chronic inflammatory conditions characterized by eosinophilic activation and may provide insight into immune dysregulation and eosinophil-associated inflammation. ECP, also known as RNase 3, belongs to the pancreatic-type ribonuclease superfamily and is predominantly stored within the secondary granules of eosinophils. The presence of anti-ECP antibodies is being investigated for its potential role in understanding eosinophil-mediated inflammation, autoimmune responses, disease mechanisms, and biomarker development in eosinophil-associated disorders.