Photothermal therapy (PTT) is an emerging cancer treatment that utilizes near-infrared (NIR) light and photoactive agents to induce localized hyperthermia, leading to cancer cell destruction. Magnetic nanoparticles (MNPs) with plasmonic properties, such as Fe₃O₄@Au hybrids, hold great potential for PTT due to their combined magnetic and optical functionalities. This study investigates the potential of Fe₃O₄@Au@PEG-OH and Fe₃O₄@Au@PEG-NH₂ core-shell nanoparticles as photoactive agents for PTT applications. The nanoparticles were synthesized and characterized for their physicochemical properties, including zeta potential and absorption spectra. Their ability to convert electromagnetic radiation into thermal energy was assessed, and their cytotoxicity was evaluated in normal and cancer cell lines (A549, MRC-5, A375, HaCaT). The effectiveness of PTT was tested at a nanoparticle concentration of 75 μg/mL under NIR laser irradiation. The results demonstrated strong NIR absorption and efficient photothermal conversion, with cytotoxicity tests confirming low toxicity in most cases. PTT treatment significantly reduced cancer cell viability, with up to a 7 % decrease in cell viability, and the highest effect was observed for the A375 cell line. These findings confirm that Fe₃O₄@Au@PEG-OH and Fe₃O₄@Au@PEG-NH₂ nanoparticles are promising photoactive agents for PTT, combining plasmonic and magnetic properties with biocompatibility.