RhoA-derived peptides have been shown to have antiviral activity against both human respiratory syncytial virus and human parainfluenza virus-3. The present study investigates the toxicity, anti-HIV-1 activity and mechanism of action of a RhoA-derived peptide (RhoA77-95). The efficacy of this peptide was compared to a scrambled peptide of the same amino acid composition and Enfuvirtide, a HIV entry inhibitor. Our data show that this RhoA-derived peptide is a non-toxic and effective inhibitor of a CXCR4 tropic strain of HIV-1. We also demonstrate that the mechanism of entry inhibition is likely mediated by polyanionic properties and is dependent on the dimerization of peptides.