Abstract <p>This study aimed to improve the bioavailability and increase the therapeutic efficacy of Hes against breast cancer by using pH and temperature-sensitive smart polymeric nanoparticles. Poly(2-hydroxyethyl methacrylate) (pHEMA) is a synthetic polymer composed of HEMA monomers, suitable for medical applications due to its biocompatibility and cytocompatibility. Vinyl imidazole and poly(<i>N</i>-isopropylacrylamide) copolymers were used to impart pH sensitivity and temperature-sensitive properties to the pHEMA polymer, respectively. Both non-loaded and hesperidin-loaded smart nanoparticles (HesSNPs) were characterized by FTIR. The particle size and size distribution of HesSNPs were determined by dynamic light scattering analysis. Scanning electron microscopy was used to determine morphological characterization. Additionally, the effects of HesSNPs on cell proliferation, apoptosis, and cell cycle in breast cancer were also examined. The MTT assay was used to evaluate the cytotoxic effects of HesSNPs on MCF-7 cells at different concentrations (10–20 µM) for 24 h. It was found that MCF-7 cell proliferation in HesSNPs-1, HesSNPs-2, HesSNPs-3, and free hesperidin group decreased statistically significantly compared to the control group, depending on the dose (<i>p</i> &lt; 0.05). The apoptotic effect was examined with the Annexin V-PI Staining Method in flow cytometry. The increase in the rate of apoptosis cells in the experimental groups was found to be statistically significant compared to the control group. Furthermore, it was determined that the nanoparticles induced apoptosis and increased the number of cells arrested in the G1 phase of the cell cycle.</p>