We studied the specific binding of an anticancer drug, dacarbazine (DTIC), to DNA bases and oligonucleotides attached to gold nanoparticles by using electrochemical methods, and the results indicate that the presence of gold nanoparticles could facilitate the binding of dacarbazine to specific DNA bases and remarkably enhance the relative detection sensitivity. The results of the study on interaction of dacarbazine with oligonucleotides also illustrate that dacarbazine could recognize some specific sequence in DNA chain and sensitively detect single-base mismatch in DNA helix.