Brain cancer is the major reason of cancer-relevant deaths every year, as it is the most challenging cancer to treat and drug delivery. Quercetin (QUR), as a flavonoid substance found in plants and fruits, has good anticancer and medicinal effects on brain tumors, but its low stability and bioavailability as well as the blood-brain barrier (BBB), prevent it from reaching brain tumors. This research has introduced a nanocomposite made of biocompatible polymers, chitosan, and carboxymethyl cellulose. This co- biopolymer's mechanical and chemical properties and drug-loading capacity have been improved by adding zinc oxide nanoparticles (ZnO NPs). In addition, graphene quantum dots (GQDs) were used to improve the chemical properties as well as the ability to penetrate the BBB. The CS/CMC/GQDs/ZnO@QUR nanocomposites have nanoneedle structures with an average size of 219.38 ± 5.21 nm and a zeta potential of −53 mV. The morphology, chemical bonds, and crystallinity of the nanocomposite were examined by FE-SEM, FTIR, and XRD analyses, respectively. By examining the release of QUR, it became apparent that the half-drug release takes about 72 h, which has a much more controlled release than other QUR carriers. Further, the MTT test on U-87 MG and L929 cell lines suggested that this nanocomposite has good anticancer properties and low cytotoxicity compared to the free QUR.