An efficient, safe and simple oligonucleotide delivery vector is necessary for gene therapy. In our previous study, a peptide-based multicomponent gene delivery system DEN-K(GALA)-TAT (DEN: a cationic poly-L-lysine dendron; GALA: endosome-disrupting peptide; TAT: TAT(48-60) cell-penetrating peptide) was optimized for plasmid DNA (pDNA) delivery. In order to improve the efficacy of this system for both siRNA (small interfering RNA) and pDNA delivery, stearic acid (SA) was introduced to produce a stearylated multicomponent peptide DEN-K(GALA)-TAT-K(SA), Circular dichroism spectroscopy demonstrated that this modification resulted in the peptide adopting more α-helical character at acidic pH, which aids endosome escape. A gel shift assay indicated that it could condense siRNA when the peptide/siRNA molar ratio was above 20. Cellular studies showed that stearylation enhanced the cell uptake significantly, with low temperature (4 °C) inhibiting its uptake. Furthermore, a gene knockdown assay performed on eGFP stable expressing HeLa cells showed that DEN-K(GALA)-TAT-K(SA) could silence eGFP expression, with a knockdown efficiency that was much better than branched PEI 25K. Further, DEN-K(GALA)-TAT-K(SA) demonstrated lower cytotoxicity than PEI 25K in an MTT assay. The stearylated multicomponent peptide DEN-K(GALA)-TAT-K(SA) is a promising siRNA delivery vector.