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Background: In the past 60 years, antibiotics have been critical in the fight against infectious diseases causedby bacteria and other microbes. Development of resistance to the antibiotics is emerging as a major publichealth issue which has resulted in the search for new antibiotics in order to maintain a pool of effective drugsat all times. Currently, there is a great interest in cationic peptides as antibiotics. These are reported to destroythe host cell membrane rather interacting with the other cell components, which may not face emergence ofresistance. In mosquitoes, peptides like cecropin, defensin and gambicin reported to have inhibitory effect onbacteria, fungi and parasites. These peptides are well-characterized at both the biochemical and molecularlevel from Anopheles and Culex species, yet their 3D structures were not reported.Methods: Defensin, cecropin and gambicin immune peptides of Culex pipiens was characterised to haveantiparasitic, antibacterial and antifungal activities. Since the crystal structure of defensin, cecropin and gambicinare not yet available their 3D structures were determined using homology modeling and Rosetta fragmentinsertion methods and were validated.Results: Stereo chemical evaluation indicated that defensin and gambicin showed that 100% residues ofconstructed model lie in the most favoured and allowed regions. Cecropin iso-forms A and B showed 100%while C showed 97.6% residues that lie in most favoured and allowed regions, which indicated quality models.Conclusion: Predicted model provide insight into their structure and aid in the development of novel antibioticpeptides.