We have synthesized the dendrimer-Au hybrid nanoclusters by solution routes, and have carried out the various spectroscopic studies in order to investigate their electronic structures. From the line-shape analyses for Au 4f core-level photoemission spectra measured with hard X-ray synchrotron-radiation of Au nanoclusters with mean diameter of 2-3 nm stabilized outside the dendrimer, it is found that Au 4f core-level photoemission spectrum consists of two components. We attribute these components to interior Au atoms and surface Au atoms bonded to dendrimers. In the valence-band photoemission spectrum of these Au nanoclusters, we have observed the bandwidth narrowing of Au 5d-derived band compared to that of bulk Au crystallite. Moreover, we have observed the characteristic spectral feature in the vicinity of Fermi level due to the dynamic final-state effect in photoemission. We have also carried out the optical spectroscopic measurements of these Au nanoclusters. From these results, we discuss the electronic structures and interfacial properties of the dendrimer-Au hybrid nanoclusters.