The heterostructure MnO-FeO nanocomposites had been successfully using Punica granatum peel extract as an excellent bioreducing species. The synthesized nanomaterials were characterised by X-ray diffraction (XRD), UV–Vis spectroscopy, SEM, EDAX, FTIR and DLS techniques. These nanocomposites can act as better nanozyme and possess a better binding affinity toward human serum albumin (HSA) in comparison to iron oxide nanopaticles (IONPs). We find that such nanocomposites exhibit high toxicity to human hepatocellular carcinoma (HUH-7) cell line and low cytotoxicity in Human hepatic cell line (WRL-68) in dose-dependent manner. The presence of different % MnO in IONPs lattice influences their activities.