<p>Bimetallic nanoparticles contain attractive properties because they show simultaneously two metals atom functions. ZnO and CeO₂ nanoparticles exhibited biocompatibility and anticancer activity properties. Therefore, we studied the anticancer effect of bimetallic nanoparticles containing ZnO and CeO₂ derived from walnut shell powder on colorectal and breast cancer cells. The ZnCeO₃, CeO₂@ZnO, and ZnO@CeO₂ NPs were synthesized from walnut shell powder and characterized and then their anticancer effects were evaluated. UV-visible spectrometry showed the peak absorbance near to361 nm. FESEM analysis determined the size of The ZnCeO₃, CeO₂@ZnO, and ZnO@CeO₂ NPs (29, 26, and 22&#xa0;nm, respectively). DPPH test showed that the nanoparticles had no profound antioxidant activity. MTT data illuminated the NPs time and dose dependent cytotoxic effects on HCT-116, MCF-7, and HUVEC cell lines. The ZnO@CeO₂ NPs showed lesser cytotoxic effect toward normal cells (IC₅₀ = 487.3&#xa0;µg/mL). AO staining and Annexin/PI test showed apoptosis induction by the nanoparticles. The real-time PCR results determined that ZnO@CeO₂ NPs caused elevation in Bax and p53 genes expression. Based on the results, ZnO@CeO₂ NPs showed shape and size dependent cytotoxic effect on the cancer cells by elevating apoptotic genes expression. Accordingly, the NPs can be considered as a good anticancer agent to treat colorectal and breast cancer cell lines.</p>