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The paper aims to investigate the cytotoxic effect on tumor cells of irradiated AuNPs in green light and subsequently functionalized with HS-PEG-NH 2. The toxicity level of gold conjugates after their functionalization with DOX and TAT peptide was also evaluated. The AuNPs were prepared using the modified Turkevich method and exposed to visible light at a wavelength of 520 nm prior their PEGylation. The optical properties were analyzed by UV-vis spectroscopy, the surface modification was investigated using FTIR and XPS spectroscopies and their sizes and morphologies were evaluated by TEM and DLS techniques. DOX and TAT peptide were linked to the surface of PEGylated AuNPs by reacting their amino groups with glycidyloxypropyl of PEGylated DOX or TAT conjugates under mild conditions at room temperature and in the presence of ethanol as catalyst. The conjugates containing DOX or DOX and TAT have been characterized by fluorescence and FTIR techniques. The changes of electrochemical features were observed using cyclic voltammetry, suggesting a better stability of irradiated nanoparticles. By mass spectrometry it was confirmed that the compounds of interest were obtained. The cell viability test showed that irradiated and non-irradiated nanoparticles coated with PEG are not toxic in normal cells. Tumor cell viability analysis showed that the PEGylated nanoparticles modified with DOX and TAT peptide were more effective than pristine DOX, indicating cytotoxicity up to 10% higher than non-irradiated ones. The presence of gold nanomaterials (AuNPs) in biomedicine and particularly in antitumor therapy still remains a topic of wide debate, as evidenced by the tremendous amount of scientific works on this issue in recent years 1-3. An impressive number of research studies have straightened their efforts toward the use of AuNPs in enhancing the efficiency of cancer treatment, due to their ease production and chemical functionalization of their surface 4,5. Gold nanoparticles are feasible to be developed as versatile nontoxic carriers for drug release as long as they are able to be conjugated with different molecules, including chemotherapeutics, antibodies, peptides, ligands, and other structures which are likely to promote a great capacity to penetrate the tumor site, resulting in a predominant accumulation of bioactive agent in the tumor region 6,7. On the other hand, the passive anticancer effect based on the accumulation strategy of AuNPs at the tumor site is limited by the inherent heterogeneities of tumor vasculature 8. It was shown that nanoparticle concentration in the target tissue is influenced by renal clearance rate, and also by activation of immune system mechanisms such as opsonization or nonspecific particle phagocytosis, fulfilled by the reticuloendothelial system (RES).