Pt mu disc electrodes have been modified by mesoporous organosilica thin films by electrochemically assisted self-assembly (EASA) of mercaptopropyltrimethoxysilane (MPTMS), tetraethoxysilane (TEOS), and the surfactant cetyltrimethylammonium bromide (CTAB). The EASA process involves the generation of hydroxide ions at the electrode/solution interface, upon the application of a cathodic current density, leading to TEOS and MPTMS polycondensation around the CTAB template and concomitant growing of a thiol-functionalized mesoporous film onto the electrode surface. The experimental conditions (current density, deposition time, silane concentration and molar ratio between surfactant template and silane) were optimised to form a thin and permeable film likely to be used in preconcentration electroanalysis. The morphology of the film electrodes were characterised by scanning electron microscopy. The permeability properties of the modified Pt mu disc electrodes have been evidenced by cyclic voltammetry using Ru(NH3)(6)(3+) as a redox probe. The best parameters identified for the film preparation are a current density of -8mAcm(-2) applied for 15s in a solution containing 110mM of hydrolysed silane precursors and 70.4mM of CTAB. Pt mu disc electrodes modified in these conditions were used for the open-circuit preconcentration of Hg(II) species prior to their detection by anodic stripping voltammetry in a mercury-free solution. In the optimized conditions, a sensitivity of 14.3mAcm(-2) mu M-1 was obtained for the 0.02-0.08 mu M concentration range. The analytical performance of such organosilica films could decay by up to two orders of magnitude for the materials prepared in conditions other than the optimized ones, highlighting the need for a fine control of the deposition parameters to elaborate sensors based on such modified ultramicroelectrodes.