Although small-interfering RNAs (siRNAs) are specific silencers for numerous disease-related genes, their clinical applications still require safe and effective means of delivery into target cells. Herein, we have developed highly efficient lipid nanoparticles (LNPs) for siRNA delivery, showcasing the advantages of novel pH-responsive lipoamino xenopeptide (XP) carriers. These sequence-defined XPs are assembled by branched lysine linkages between cationizable polar succinoyl tetraethylene pentamine (Stp) units and apolar lipoamino fatty acids (LAFs) at various ratios into bundle or U-shape topologies. Integrating of LAF₄-Stp₁ XPs into siRNA-LNPs at an optimized molar ratio led to robust cellular uptake, high endosomal escape, and successful in vitro gene silencing activity at extremely low (150 picogram) siRNA dose. Of significance is functional in vivo endothelium tropism of siRNA-LNPs with bundle LAF₄-Stp₁ XP after systemic injection into mice, demonstrated by superior knockdown of liver sinusoidal endothelial cell (LSEC)-derived FVIII in comparison with MC3-based LNPs, but moderate silencing of hepatocyte-derived FVII. Optimizing lipid composition following Click-modification of siRNA-LNPs with ligand cRGDfk efficiently silenced vascular endothelial growth factor receptor-2 (VEGFR-2) in xenograft tumor endothelial cells (TECs). Our findings shed light on the role of ionizable XPs in the LNP in vivo cell-type tropism, laying the groundwork for future therapeutic application.