A study of the reductive desorption process of 6MP-coated Hg and Au(111) electrodes in alkaline media has been carried out by means of such electrochemical techniques as cyclic voltammetry, chronoamperometry, and capacity-potential curves. The cyclic voltammograms show a single reduction peak whose peak potentials are strongly dependent on the nature of the substrate, Hg and Au(111) in this study. The full widths at half-maximum (fwhm) for Hg and Au(111) electrodes respectively are 19 and 21 mV at a scan rate of 0.1 V/s. These values are generally indicative of the existence of strong lateral interactions between molecules. The chronoamperometric curves have been recorded by single potential step experiments from a potential where the monolayer is stable to different final values within the range of potential where the monolayer is being desorbed. The curve shapes resemble those of systems that follow nucleation and growth mechanisms in the formation or dissolution of two-dimensional layers. In fact, the curve analysis using the nucleation and growth model of etching centers which was carried out in this report is actually in agreement with a mechanism of this kind for the dissolution of the 6MP monolayer at Hg and Au(111) electrodes. This study compares the properties of the 6MP monolayer at the two substrates Hg and Au(111) as well as with other thiol derivative monolayers.