Abstract. The synthesis of a new class of hybrid materials with two differently oriented layers of calcite at adjacent sides of an organic template is demonstrated. A Langmuir monolayer of the amphiphilic block copolymer poly(butyl acrylate)-b-poly(hydroxypropyl acrylate) directs the formation of a first CaCO 3 phase through interaction with the hydrophilic poly(hydroxypropyl acrylate) blocks. After partial hydrolysis of the hydrophobic poly(butyl acrylate) segments a second CaCO 3 phase is formed on the monolayer associated to the first mineral phase. Thus, bilayered CaCO 3 -based hybrid materials are obtained with two differently oriented calcite phases at opposite sides of the polymer film. By using DNA as an additive the crystal orientation in the second layer can be modified.