Single molecular conductances of alkanethiols with different lengths were determined by conducting-atomic force microscopy with large gold nanoparticles (5.4 nm diameter) as the contact. Because of the large size of the nanoparticles, the Coulomb blockade effect is small and the quantized level effect is negligible. These effects were the problems with small nanoparticles (1.5 nm) in analysis of the current-voltage data. Therefore, the measurements with large nanoparticles gave the reasonable conductances and reasonable distance dependence that agree well with the scanning tunneling microscopy repeated break-junction results.