KRAS mutations are one of the most common oncogenic driver mutations in human cancers, including non-small cell lung cancer (NSCLC), and have established roles in cancer pathogenesis and therapeutic resistance. The development of effective inhibitors of mutant KRAS represents a significant challenge. Three-way junction (3WJ)-based multi-functional RNA nanoparticles have the potential to serve as an effective in vivo siRNA delivery platform with the ability to enhance tumor targeting specificity and visualize biodistribution through an imaging moiety. Herein, we assembled novel EGFRapt-3WJ-siKRASG12C mutation targeted nanoparticles to target EGFR-expressing human NSCLC harboring a KRASG12C mutation to silence KRASG12C expression in a tumor cell-specific fashion. We found that EGFRapt-3WJ-siKRASG12C nanoparticles potently depleted cellular KRASG12C expression, resulting in attenuation of downstream MAPK pathway signaling, cell proliferation, migration/invasion ability, and sensitized NSCLC cells to chemoradiotherapy. In vivo, these nanoparticles induced tumor growth inhibition in KRASG12C NSCLC tumor xenografts. Together, this study suggests that the 3WJ pRNA-based platform has the potential to suppress mutant KRAS activity for the treatment of KRAS-driven human cancers, and warrants further development for clinical translation.