An effective electrochemical sensor was constructed using an unmodified boron-doped diamond electrode for determination of genistein by square-wave voltammetry. Cyclic voltammetric investigations of genistein with HClO4 solution indicated that irreversible behavior, adsorption-controlled and well-defined two oxidation peaks at about +0.92 (P-A1) & +1.27 V (P-A2). pH, as well as supporting electrolytes, are important in genistein oxidations. Quantification analyses of genistein were conducted using its two oxidation peaks. Using optimized experiments as well as instrumental conditions, the current response with genistein was proportionately linear in the concentrations range of 0.1 to 50.0 mu g mL(-1) (3.7x10(-7)-1.9x10(-4) mol L-1), by the detection limit of 0.023 mu g mL(-1) (8.5x10(-8) mol L-1) for P-A1 and 0.028 mu g mL(-1) (1.1x10(-7) mol L-1) for P-A2 in 0.1 mol L-1 HClO4 solution (in the open circuit condition at 30 s accumulation time). Ultimately, the developed method was effectively applied to detect genistein in model human urine samples by using its second oxidation peak (P-A2).