In a 0.02 mol/L Na2HPO4-KH2PO4(PBS) buffer solution(pH=6.82), the electrochemical behavior of mitoxantrone was studied by linear-sweep voltammetry and cyclic voltammetry at a Pt/C ion implantation modified microelectrode. A sensitive reduction peak was observed. The peak potential was -0.72 V(vs.SCE), the peak current was proportional to the concentration of mitoxantrone within the ranges of 7.0×10-8-9.0×10-7 mol/L and 1.0×10-6-2.4×10-5 mol/L, with a detection limit of 4.0×10-8 mol/L. The linear correlation coefficients were 0.9994 and 0.9992, respectively. This method has been applied to the direct determination of mitoxantrone in simulated urine. The recoveries were in the range from 96.2% to 105.9%. The reduction process was a quasi-reversible one with adsorptive characteristics at the Pt/C microelectrode. The electrode reaction rate constant ks and the electron transfer coefficient α of the system were determined to be 4.5 and 0.65 s-1, respectively. The experiments showed that Pt element had surely been implanted into the surface of the carbon fiber, and the atomic Pt improved the electrocatalytic activity. The Pt/C microelectrode had a good stability and reproducibility.