Abstract: A method and kit for electrochemically simply determining with excellent precision the amount of double-stranded DNA does not require an expensive measurement electrode, such as an immobilized enzyme electrode or any high level electrode production technique which can retain uniform surface area accuracy. A method and kit are provided for electrochemically determining the amount of double-stranded DNA in a sample solution based on a residual amount of a substance capable of binding to the double-stranded DNA which is added to the solution in excess amount, in which a buffering substance is added to a sample solution, the buffering substance being capable of allowing an oxidation wave potential of the potential-current curve for the substance capable of binding to the double-stranded-DNA determined in a solution containing the buffering substance to change depending on the concentration of the free substance capable of binding to the double-stranded DNA in the solution.