Size-dependent quantized double layer (QDL) charging of dodecanethiol monolayer-protected diffusing silver nanoparticles (MP-AgNPs) is reported. Multiple periodic peaks in the differential pulse voltammograms were observed for the MP-AgNPs in a size range of 2.7 nm to 5 nm and these are attributed to the QDL charging of monolayer-protected clusters. The potential difference between successive peaks decreases with an increase in the MP-AgNPs’ size. The potential of zero charge (EPZC) as a function of size was determined from the intercept of a Z-plot, which shifted towards more negative potential with increasing size. Voltammetric measurements on smaller size MP-AgNPs (1.7 nm) did not show any QDL charging peaks due to the oxide layer associated with them.