An ethylenediamine fixed humic acid preparation (EHA) was synthesized by the interaction between the etheride of humic acid(HA) and ethylenediamine. The EHA was characterized by Fourier transform infrared spectrometry and elemental analysis, and employed to prepare a chemically modified electrode. Based on EHA-containing carbon paste electrode, the accumulation and electrochemical behavior of gold(III) were investigated by cyclic voltammetry and differential pulse stripping voltammetry (DPSV). The proposed measurement involves a medium exchange procedure in which the preconcentration step was accomplished in a solution of 0.35 M HCl and the subsequent electrochemical step performed in a supporting electrolyte of 0.8 M HCl. The oxidizing current (I'pa2) obtained by DPSV was proportional to the concentration of the Au(III) ion in a range of 3.5×10-6～5.1×10-8 M. The sensitivity and selectivity of the proposed method are obviously better than that of results obtained by using a chemically modi®ed carbon paste electrode of ordinary HA.