The current study investigates the anticancer effects of PEGylated chitosan nanoparticles (CS NPs) coloaded with betaine (BT) and nedaplatin (ND) on breast adenocarcinoma (MCF-7) cells and breast cancer-bearing rats. Hereof, the ionotropic gelation approach was implemented for the synthesis of PEG-uncoated and PEG-coated CS NPs encompassing either BT, ND, or both (BT-ND). The sizes of the developed BT/CS NPs, ND/CS NPs, and BT-ND/CS NPs were 176.84