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, the 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-2-tetrazolium 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.