<p>Disclosed is a determination method which can quantify a specific protein or peptide contained in a trace amount with high accuracy and in a simple manner without the need of using any expensive reagent. A protein or peptide of interest can be quantified by LC/MS/MS by using, as an internal standard, a protein or peptide comprising an amino acid sequence having the reshuffling the binding order of amino acid residues in the amino acid sequence for the protein or peptide of interest.</p>
