The thermal stability of cytochrome c (cyt c) after Au-nanoparticle-directed association has been studied by various spectroscopic (electronic absorption, resonance Raman, and circular dichroism) and electrochemical methods. The results show that the thermal stability of the Au-cyt c superstructure biocomposite formed by the electrostatic and hydrophobic interactions among the associated proteins increases significantly. It is mainly caused by strong hydrophobicity of the associated cyt c in Au-cyt c superstructure at high temperature, which results from the compact secondary structure and the packing of hydrophobic side chains around the Trp 59 and heme. In addition, the formation of bis-His configuration of heme is facilitated by the tightly self-associated state of cyt c in the Au-cyt c superstructure. The electrostatic coupling of the opposite charges among shells of the adsorbed proteins due to the formation of the superstructure biocomposite can reduce repulsions among the same charges in protein. These factors are also important for enhancing the stability of the associated cyt c. Furthermore, the voltammetric behavior of Au-cyt c at DNA modified glassy carbon electrode has been investigated for extending the application of Au-cyt c.