In this study, zeolite–copper oxide/graphene oxide nanocomposites were synthesized and characterized as carriers for the anticancer drug Doxorubicin (DOX). The morphology, crystalline structure, and functional groups of the samples were investigated using analytical techniques such as SEM, TEM, XRD, and FTIR. According to XRD analysis and the Williamson–Hall method, the crystallite size of pure copper oxide (CuO) nanoparticles was found to be 15–30 nm, while that of graphene oxide (GO) ranged between 1–5 nm. In the ternary nanocomposite, the CuO crystallite size significantly decreased to 3–15 nm, indicating the strong inhibitory effect of the combined zeolite and GO matrix on nanoparticle growth, resulting in a structure suitable for controlled drug release. Drug loading efficiency was determined based on adsorption capacity, and the release profile was evaluated under physiological (pH = 7.4) and acidic (pH = 5.5) conditions over 72 hours. The results demonstrated that the zeolite–CuO/GO exhibited a more controlled release of DOX at pH=7.4, while an explosive and enhanced release was observed under the acidic pH=5.5 condition, simulating the tumor microenvironment. Cytotoxicity assessment revealed that the drug-free components (zeolite, nanocomposites, and GO) showed very low toxicity toward HS-578T cells (IC50 > 100 µg/mL). However, after loading with DOX, the toxicity of all samples increased significantly. Notably, the DOX-loaded zeolite–CuO/GO nanocomposite exhibited the highest cytotoxicity, with the lowest IC50 value (37.12 µg/mL), indicating its superior efficacy in inhibiting cancer cell growth. Apoptosis assays confirmed that the drug-loaded nanocomposite significantly induced programmed cell death. These findings collectively confirm the high potential of the developed nanocomposite for targeted drug delivery and reduced systemic side effects.