Background and Objective: The 4T1 murine breast cancer cell line is commonly employed to study breast cancer metastasis. Transfections to this cell line are frequently carried out using lipid/polymer based gene delivery vehicles. The research paper attempts to use peptide based transfecting agents Str-R8 and MTS-AR8 for in vitro transfection of 4T1 cells.Methods: These peptides were investigated previously by the authors and showed comparable plasmid DNA complexation abilities. The efficiency of Str-R8, MTS-AR8 in delivery of the plasmid DNA, pSFCMV- SEAP to 4T1 cells is compared to the cationic lipid reagent Lipofectamine®3000. Transfection was measured by estimating the ability of the expressed reporter gene i.e., secreted alkaline phophatase to cleave the substrate para-Nitrophenylphosphate to para-Nitrophenol. Results: Transfection of 4T1 by MTS-AR8/pSF-CMV-SEAP was twofold greater than that mediated by Str-R8/pSF-CMV-SEAP (probability of the values being similar; p<0.05) and comparable to Lipofectamine ®3000/pSF-CMV-SEAP (probability of the values being similar; p>0.5) at a peptide basic amino acid per nucleic acid phosphate ratio of 5:1. Increasing the peptide basic amino acid per nucleic acid phosphate ratio, of MTS-AR8 resulted in a decrease in the transfection of 4T1 cells (probability of the obtained values being similar; p <0.06). Conclusion: The MTS-AR8 peptide has potential and can be further investigated for nucleic acid delivery involving the 4T1 cell line.