A poly(L-methionine)/graphene modified glassy carbon electrode was prepared.Experiments showed that the modified electrode exhibits an obvious electrocatalytic ability for the oxidation of guanine in 0.1 mol/L phosphate buffer solution(pH 7.0).Effects of pH value and scan rate on electrochemical behaviors of guanine were investigated by cyclic voltammetry.The detection of guanine was performed by differential pulse voltammetry.The result indicated that the oxidation peak current of guanine was linear with its concentration in the range of 3.6×10-7-4.0×10-5 mol/L, with a correlation coefficient(r) of 0.990 4 and a detection limit(S/N=3) of 5.0×10-8 mol/L.The modified electrode had a good stability and reproducibility.