The main idea in this research used quercetin (QT) as a stabilizing agent to prepare CuO nanoparticle (NPs). QT is a pigment which exists from plants, fruits, and in some medicines. It contains numerous hydroxyl groups, works as a complexing agent and a self-assembly agent. The prepared CuO-NPs were characterized by Fourier transformed infrared (FT-IR), X-ray diffraction (XRD), scanning and transmission electron microscopy (SEM and TEM), and energy-dispersive X-ray analysis (EDX). The structure investigation confirm that the CuO-NPs were polycrystalline nature having a monoclinic crystalline form and showed (111̅ ) and (111) preferential orientations. The estimated particle sizes by XRD, TEM, and SEM ranged from 12.03 to 15.3 nm. Surface analysis displayed that homogeneously distributed CuO-NPs with a spherical shape. On the other hand, synthesized CuO-NPs were tested for anticancer activity on the human breast. The infected cell (MCF-7) uses MTT (3-(4,5-dimethyl-2-triazolyl)-2,5-diphenyl-2tetrazolium bromide) test. The inferred CuO-NPs clarify high anticancer cytotoxicity of the (MCF-7) with an IC50 μM value of 57.6 and 42.8 µg/mL for 24 and 72 h respectively.