Antimicrobial peptides (AMPs) are a novel class of therapeutics with activity against bacteria. Such peptides mostly act by disrupting bacterial cytoplasmic membrane. Therefore, membrane composition as well as peptide properties are both important in determining a peptide’s level of activity. Such peptides may have both positive and negative additional properties. Therefore, new peptides with better and enhanced properties are being developed. One of such peptides is OP-145, derived from LL-37. From OP-145, new AMPs were developed, including P148 and P276, which were researched in this thesis. OP-145, P148 and P276 were subjected to a series of test which included in silico modelling and investigation of their interactions with prokaryotic and eukaryotic model membranes by terms of thermoanalytical measurements using DSC, measurements of size of model membrane vesicles in interaction with peptides using DLS, determination of peptides’ secondary structure in interaction with membranes using CD and quantitative research of the peptides’ ability to disrupt these membranes in the form of leakage assays using fluorometry. Data gained from these experiments was then compared to previously known properties of the peptides. Results have shown a stronger level of activity of P148 and P276 in comparison to OP-145 towards both bacterial and mammalian model membranes. It was concluded that P148 and P276 have better biophysical properties than OP-145 in terms of antimicrobial activity, but that further research is needed in order to better understand their properties and possible therapeutic use.