A cross-linked amphiphilic polymethacrylate, composed of hydrophobic octanal-derived acetal and hydrophilic poly(ethylene glycol) moieties, was synthesized with different degrees of hydrophilicity. The polymer hydrophilicity was estimated based on measurements of contact angles with water. Release of octanal was achieved in a biphasic system composed of hexane and an aqueous suspension of the polymers. The acetal moieties of the polymers were gradually hydrolyzed in an acidic solution, releasing octanal continuously for 600 h. The amount of released octanal increased with an increase in the hydrophilicity of the polymer under acidic conditions.