In perpendicularly magnetized Pd/Co/Pd trilayers, the hydrogenation not only increased Kerr signal but also significantly enhanced the magnetic coercivity (H C ) by 17%. The reversibility was demonstrated by cyclic H2 exposure. The time constants of hydrogen absorption and desorption effect on H C range from tens to hundreds seconds, depending on the H2 gas pressure. The magneto-optical Kerr signal and magnetic coercivity was simultaneously recorded during H2 absorption and desorption. These multifarious signals respond differently and provide a detailed understanding of hydrogenation effect on the functional Pd/Co/Pd trilayers.