Antimicrobial peptides (AMPs) are an essential part of innate immune defense against microbial infection. Naturally occurring AMPs are basic peptides composed of 12–50 amino acids that are ubiquitously distributed throughout all kingdoms of life. AMPs display extensive sequence heterogeneity; however they do share a number of common characteristics, including a net positive charge of ≥+2 (with +4 to +6 being most common), 50%–70% hydrophobic amino acids, and a propensity to fold into amphipathic conformations in the presence of membranes. AMPs display a broad spectrum of antimicrobial activity against both Gram-negative and Gram-positive bacteria, fungi, and enveloped viruses , so they are studied as new alternative to common antibiotics because pathogens have developed resistance [1, 2]. The type and number of AMPs in mammals varies from species to species; a class of peptides present in most of these organisms are the Defensins. Defensins are small cysteine-rich cationic proteins found in both vertebrates and invertebrates. They have also been reported in plants. They are active against bacteria, fungi and many enveloped and nonenveloped viruses and consist of 18-45 amino acids including six to 8 conserved cysteine residues. This work is focused on characterization of interaction of HNP-1 (human neutrophil peptide 1), a peptide belonging to the family of human α- Defensin, with model membranes. This AMP is characterized by three β-sheets and one β-hairpin and the structure is strongly stabilized by three disulfide bonds between cysteine residues and a salt bridge between arginine and glutamic acid. At physiological pH the peptide has the total charge equal to +3, conferred by three cationic residues arginine. The activity threshold ratio between HNP-1 and LUV (Large Unilamellar Vesicle) and the capability of this antimicrobial peptide to penetrate into phospholipidic bilayer system has been tested using Circular Dicroism, Fluorescence emission spectroscopy and membrane spin labelling Electron Paramagnetic Resonance.