Pressure-area isotherms of ternary component monolayers of nucleobase amphiphiles, octadecylcytosine (C-18-Cyt) and diacetylene-containing adenine and thymine amphiphiles (DA-Ade, DA-Thy), were changed by addition of oligonucleotides, d(GT)(15) or d(GGT)(10), in the water subphase. Photopolymerization of diacetylene in the monolayer was strongly suppressed on the oligonucleotide subphase. This suggests that the oligonucleotide can act as a template for the diacetylene monomer arrangement via complementary hydrogen bonding at the air-water interface.