Delivery of small interfering RNA (siRNA) as a therapeutic tool is limited due to critical obstacles such as the cellular barrier, the negative charges of the siRNA molecule, and its instability in serum. Several siRNA delivery systems have been constructed using cell-penetrating peptides (CPPs) since the CPPs have shown a high potential for oligonucleotide delivery into the cells, especially by forming nanoparticles. In this study, we have developed a new family of short (15mer or 16mer) tryptophan-(W) and arginine-(R) rich Amphipathic Peptides (WRAP) able to form stable nanoparticles and to enroll siRNA molecules into cells. The lead peptides, WRAP1 and WRAP5, form defined nanoparticles smaller than 100 nm as characterized by biophysical methods. Furthermore, they have several benefits as oligonucleotide delivery tools such as the rapid encapsulation of the siRNA, the efficient siRNA delivery in several cell types, and the high gene silencing activity, even in the presence of serum. In conclusion, we have designed a new family of CPPs specifically dedicated for siRNA delivery through nanoparticle formation. Our results indicate that the WRAP family has significant potential for the safe, efficient, and rapid delivery of siRNA for diverse applications.