The electrochemical responses of cytochrome c on the gold electrodes modified with nucleic acid base derivatives such as 2-amino-6-purinethiol. 2-amino-6-mercaptopurine riboside. 6-amino-8-purinethiol and 2-thiouracil were investigated. The monolayers of 2-amino-6-purinethiol and 6-amino-8-purinethiol on gold can promote the electron transfer between cytochrome c in solution and gold electrode like that of well-known promoters such as pyridylthiol derivatives and carboxylic acid terminated alkanethiols, as reported previously. However, in the case of 2-amino-6-mercaptopurine riboside modified gold electrode, the redox response of cytochrome c was completely inhibited, because a bulky ribose group inhibited the promoting ability. We also confirmed that the 2-thiouracil on gold electrode can facilitate the electron transfer between cytochrome c and gold electrode. The redox response of cytochrome c on 6-amino-8-purinethiol modified Sold electrode was inhibited effectively by forming a hydrogen bonded complex with a complementary nucleic acid base derivative, thymidine. However, in the cases of 2-amino-6-purinethiol and 2-thiouracil modified gold electrodes, the redox response of cytochrome c was not inhibited by thymidine treatment. These phenomena should reflect the difference of adsorbed direction between 2-amino-6-purinethiol and 6-amino-8-purinethiol on gold and the unsuitable matching of thiouracil adsorbed on gold with thymidine in solution.