Abstract: Graphene/Cu-Ag composites were prepared by a simple stirring reduction procedure. A novel electrochemical sensor was developed based on graphene/Cu-Ag composites modified glassy carbon electrode. The as-prepared graphene/Cu-Ag composites were characterized by scanning electron microscope and  transmission electron microscope. The electrochemical behaviors of guanine and adenine on the modified electrode were investigated by cyclic voltammetry and differential pulse voltammetry. The results showed that the graphene/Cu-Ag composites film greatly accelerate the electron transfer of the analytes on the electrode in 0.1 mol/L pH 4.5 acetate buffer solutions. The concentration of guanine and adenine showed good linear relationships with the oxidation peak current in the range of 1.0~100.0 μmol/L with correlation coefficients of R = 0.997 and 0.998, respectively. The limits of detection for guanine and adenine were 6.0×10  8mol/L and 5.0×10-8 mol/L (S/N= 3), respectively. Furthermore, the measurements of thermally denatured single stranded DNA with the asprepared sensor were carried out and the value of (G+C)/(A+T) of singlestranded DNA was calculated to be 0.79.