The electrochemical properties of gold electrodes modified with 2-amino-6-purinethiol and 6-amino-8-purinethiol were investigated. The aminopurinethiolate monolayers could facilitate the electron transfer between cytochrome c in solution and a gold electrode in the same way as well-known promoters such as pyridylthiol derivatives and carboxylic acid terminated alkanethiols as reported previously. The redox response of cytochrome c on a 6-amino-8-purinethiol modified gold electrode was inhibited effectively by forming a hydrogen bonded complex with a complementary nucleic acid base derivative, thymidine. However, in the case of a 2-amino-6-purinethiol modified gold electrode, an inhibition of the redox response of cytochrome c by thymidine treatment was not observed. These phenomena reflect the difference of direction of each of the adsorbed molecules.