Cell-penetrating peptides (CPPs) are a potential tool for intracellular delivery of different kinds of cargoes. Because of their growing use in nanobiomedicine, both for diagnostics and for treatment, metal nanoparticles are an interesting cargo for CPPs. Here, gold nanoparticles (AuNps) and the amphipathic proline-rich peptide SAP have been used. Conjugation of the peptide onto the AuNps was achieved by addition of a cysteine to the SAP sequence for thiol chemisorption on gold, and the attachment was confirmed by visible spectroscopy, dynamic light scattering (DLS), zeta-potential (ZP), stability towards ionic strength (as high as 1 M NaCl), X-ray photoelectron spectroscopy (XPS) and high-resolution transmission electron microscopy (HR-TEM) coupled to electron energy loss spectroscopy (EELS). AuNp-C-SAP internalization in HeLa cells was observed by three different microscopy techniques-TEM, confocal laser scanning microscopy (CLSM) and transmission X-ray microscopy (TXM)-and all of them have confirmed the effective intracellular delivery of AuNps by SAP.