Background: Standard treatment for metastatic colorectal cancer (mCRC) is systemic chemotherapy with anti-EGFR treatment, depending on KRAS mutational status. However, tumors harboring a KRAS mutation do not respond to existing targeted therapy. Moreover, targeting mutant KRAS has, to date, not been possible. Herein, we explore using a KRAS inhibitory nanoparticle (NP), to directly knock down mutant KRAS. Methods: Utilizing fluorescent-labeled small interfering RNA (siRNA) NPs, uptake was assessed via fluorescent microscopy. KRAS mutant CT26 and wild-type MC38 CRC cell lines were incubated with either scramble (Sc) sequence siRNA NP, KRAS siRNA NP, or FOLFOX (fluorouracil + oxaliplatin) chemotherapy ± KRAS siRNA NP. Cell viability was assessed via a luminescent viability assay. KRAS and cleaved caspase 3 protein expression were assessed using western blotting. Results: Fluorescent NP uptake was demonstrated in CT26 cells as early as 260 minutes post treatment, with increased uptake through 780 minutes. Decreased cellular viability was seen with KRAS siRNA NP treated CT26 cells, as compared to both Sc siRNA NP and non-treated CT26 cells (both p < 0.0001). Cell viability was significantly diminished with FOLFOX combined with KRAS siRNA NP as compared to FOLFOX alone for CT26 cells (p = 0.0003), but not MC38 cells (p = 0.2259). Western blot demonstrated decreased KRAS and increased cleaved caspase 3 expression in CT26 cells treated with KRAS siRNA NP. Conclusions: A KRAS siRNA tagged NP was internalized by the CRC cells in vitro, and induced cellular death via apoptosis in mutant type KRAS CRC. In addition, KRAS siRNA NP acted synergistically with FOLFOX chemotherapy to enhance cell death. We believe KRAS inhibition based NP treatment is a promising target for mutant type KRAS CRC.