An electrochemical detection system for DNA has been investigated based on the current increase due to the catalytic oxidation of hydrogen peroxide with platinum deposited by the electrochemical reduction of chloro-2,2':6',2''-terpyridine platinum (II) chloride dihydrate (Pt complex) on a screen-printed carbon electrode. The platinum deposited on the screen-printed carbon electrode that has shown no catalytic activity for oxidation of hydrogen peroxide gives rise to catalytic activity. Cyclic voltammetry was used to reduce the Pt complex to deposit platinum metal on the carbon electrode. The oxidation current of hydrogen peroxide increased with increasing concentration of the Pt complex in the electrolytic deposition. The intercalation of the Pt complex into double-stranded DNA (dsDNA) decreased the concentration of free Pt complex and caused a decrease in the diffusion coefficient of the intercalated Pt complex. Moreover, the reduction of the Pt complex was inhibited due to steric hindrance. Thus, the oxidation current for hydrogen peroxide by platinum deposited on the carbon electrode decreased with an increase in the concentration of dsDNA. This procedure is absolutely simple without the need to immobilize DNA. Furthermore, the use of inexpensive screen-printed carbon electrodes will allow for the development of disposable sensing systems.