We examined charge transport properties of two gold nanoparticles (GNPs) in a nanogap transistor with a gap width of ∼10 nm. The GNPs connected to each other and to outer electrodes through a small number of dithiolated terthiophene wire molecules as a tunneling barrier. The transport property measured at 11 K was analyzed based on the theory of double-dot single-electron transistors and inelastic cotunneling. The results clearly show mutual Coulomb interactions between the two GNPs. Moreover, we found the appearance of superperiodic conductance, because of differences in the charging energy of the two GNPs.