A hexyl acrylate monolith was prepared via photopolymerization into a cyclic olefin copolymer micro-device for reversed-phase electrochromatography purposes. This work deals with the influence of the irradiation conditions (irradiation time and light intensity) used during synthesis on the electrochromatographic performances of the monolithic column obtained. Up to day, the monolith structure was often controlled by means of irradiation time at constant light intensity, but the effect of light intensity (irradiance) on the monolith structure was scarcely considered. This study shows a strong effect of light intensity on electrochromatographic efficiency. Using an optimal light intensity of 4.7 mW/cm 2 and an irradiation time of a few minutes allows obtaining heights equivalent to a theoretical plate reaching down to 5 m for the reversed-phase separation of six polycyclic aromatic hydrocarbons.