We report an efficient method for the fabrication of a single electron transistor (SET) using DNA-assisted assembly of nanoparticles. In this method, the DNA molecules function not only as the assembler, but also as the modulator for the electron tunneling behaviors of single electron transistors. A study of the assembly between an Au nanoparticle (∼10nm) and various lengths of DNA molecules confirms the effectiveness of this method in creating a SET. Most devices exhibited clear single electron effects.