In a 0.10 mol/L Hac-NaAc buffer solution(pH= 4.59), a sensitive reduction peak of bleomycin was observed by linear sweep voltammetry at a Co/GC ion implantation modified electrode. The peak potential was -0.73 V(vs. SCE). The peak current was proportional to the concentration of bleomycin over the range of 5.0 × 10-8-1.0 × 10-6 and 1.0 × 10-6-1.0 × 10-5mol/L with a detection limit of 2.0 × 10-8 mol/L. The electrochemical behavior of the reduction peak of bleomycin at the Co/GC modified electrode was studied by linear sweep and cyclic voltammetry and applied to the determination of bleomycin in urine. This method is simple,rapid and reliable. The reduction process is quasi-reversible. The experiments of AES and XPS showed that Co was surely implanted into the surface of GCE and the depth distribution of Co was ingood agreement with Gooses normal distribution; the implanted Co at GCE improved the electrocatalytic activity.