The electrochemical deposition of transition metal chalcogenides thin films has received recently much attention due to their potential applications in electrocatalysis. Among them the special attention is focused on cobaltselenium system. Usually, thin films of these materials are prepared by hydrothermal synthesis or high temperature and vacuum techniques. However electrodeposition has been found to be a very good and low-cost method to fabricate thin polycrystalline films of these compounds. The electrodeposition of thin films of polycrystalline Co-Se system from aqueous baths was studied. The experiments were carried out following the thermodynamic analysis. A conventional three-electrode cell: Cu as working electrode, Ptsheet as counter electrode and Saturated Calomel Electrode (SCE) as reference electrode was used. The electrodeposition mechanism of pure elements Se, Co and Co-Se phases on copper substrate was studied by chronoamperometry, cyclic voltammetry and hydrodynamic techniques. Additionally, chronoamperometry and cyclic voltammetry were combined with electrochemical quartz crystal microbalance to analyse this process in details. This work was supported by the Polish National Center of Science under grant 2016/21/B/ST8/00431.