Abstract We measured the permittivity (imaginary component of dielectric constant) and the conductivity of gold nanoparticles cross-linked with dithiol spacer molecules in the ac frequency range of 300Hz to 3MHz. The different sized gold nanoparticle colloids we used were 20 nm, 13 nm, 10 nm and 5 nm diameter. The gold nanoparticles were cross-linked with 1,6-Hexanedithiol, which has a sulfur atom on its each end that can bind strongly to gold to form a molecular junction. The combination of the four different size gold nanoparticles and the same spacer molecules led to four kinds of samples. Using a simple equivalent RC circuit model to fit the conductivity relaxation time of the disordered Au cluster network, we estimate that the conductivity relaxation time for each kind of sample is about 100ns at room temperature.