Marine gastropod, Peronia peronei, from north of the Persian Gulf, protein extraction was investigated using ultrafiltration, reversed-phase high-performance liquid chromatography and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF/TOF). The mass spectra showed that, the isolated peptide is most probably Dolabellanin B2 that has been extracted before from other marine mollusk, Dolabella auricularia. The antibacterial activity of purified peptide was assessed against seven bacterial strains (Staphylococcus aureus, Bacillus subtilis, Serratia marcescens, Escherichia coli, Klebsiella pneumoniae, Pseudomonas aeruginosa and Proteus mirabilis). Broth micro-dilution method, standard disk diffusion assay and bioautography were used for this aim. According to the results the identified peptide showed strong antibacterial activity against all mentioned bacterial strains. Computational studies through peptide modeling servers followed by 50 ns molecular dynamics simulation and surface electrostatic calculations indicates that this sequence could be most probably related to alpha helical cationic antimicrobial peptides (alpha-CAMPs) with overall charge of +1 at pH 7.