OBJECTIVE: The goal of this study was to evaluate the long-term behavior of the surface electrode through electrochemical characterization and follow up of implanted parylene/platinum microelectrodes. APPROACH: To this aim, we designed and manufactured specific planar electrodes for cortical implantation for a rat model. This work was included in the INTENSE® project, one of the goals of which was to prove the feasibility of selective neural recording or stimulation with cuff electrodes around the vagus nerve. MAIN RESULTS: After a 12-week implantation on a rat model, we can report that these microelectrodes have withstood in-vivo use. Regarding the biocompatibility of the electrodes (materials and manufacturing process), no adverse effect was reported. Indeed, after the three months implantation, we characterized limited tissue reaction beneath the electrodes and showed an increase and a stabilization of their impedance. Interestingly, the follow up of the electrochemical impedance combined with electrical stimulation highlighted a drop of the impedance up to 60% @1kHz after ten minutes of electrical stimulation at 110Hz.