This paper recommends a useful procedure for digesting the blood sample and discusses the optimum working conditions for determinations of whole blood selenium and serum selenium by cathodic stripping voltammetry. The blood sample is heated with the mixture of HNO3-HClO4to destroy protein contents, and then HCl is used to reduce Se(VI) for the stripping measurement. Considering the matrix effects, the method of addition is preferred. Stripping peak potential, -0.5 v vs.Ag/AgCl. With the stripping peak current the linear working range for selenium is 0.1 – 12 ppb and 0.1 ppb is the detection limit. This method is highly sensitive, having fairly good repeatability. Coefficient of variation 3.97%. Recovery 91% – 108%. It has been applied to clinical analysis of which the results are satisfactory.