Abstract: The glassy carbon electrode (GCE) was modified with polythionine (PTh) to form PTh/GCE by electropolymerization of thionine with cyclic voltammetry, and nanoparticles of gold were adhered to the PTh/GCE through coordination and electrostatic action of the PTh layer to form the modified electrode of AuNP′s/PTh/GCE. Finally, DNA probe was immobilized onto the AuNP′s/PTh/GCE through the interaction between ss-DNA and nano-gold to form ss-DNA/AuNP′s/PTh/GCE, which was further hydridized in cDNA solution at 42 ℃ to form ds-DNA/AuNP′s/PTh/GCE. The immobilization and hydridization of DNA were characterized by differential pulse voltammetry and AC impedance spectroscopy in a solution of ［Fe(CN)6］3-/4-. It was found that linear relationship between values of detection signals (ΔRet) and concentration of the 20-base PAT genetic sequence was obtained in the range of 1.0×10-10-1.0×10-6mol·L-1. Detection limit (3s) of this biosensor was found to be 3.2×10-11mol·L-1.